Azadirachtin affects the circadian rhythm of locomotion in Leucophaea maderae

Abstract

Azadirachtin shortens the period length of the locomotor activity rhythm in the circadian rhythm of Leucophaea maderae and induces splitting of this rhythm in two components in about 40% of the animals. The phase relationship between the two components is 180°. Both shortening of period and splitting are more pronounced in animals possessing longer periods before the injection of azadirachtin.     

The circadian rhythm controls telomeres and telomerase activity

Circadian clocks are fundamental machinery in organisms ranging from archaea to humans. Disruption of the circadian system is associated with premature aging in mice, but the molecular basis underlying this phenomenon is still unclear. In this study, we found that telomerase activity exhibits endogenous circadian rhythmicity in humans and mice. Human and mouse TERT mRNA expression oscillates with circadian rhythms and are under the control of CLOCK–BMAL1 heterodimers. CLOCK deficiency in mice causes loss of rhythmic telomerase activities, TERT mRNA oscillation, and shortened telomere length. Physicians with regular work schedules have circadian oscillation of telomerase activity while emergency physicians working in shifts lose the circadian rhythms of telomerase activity. These findings identify the circadian rhythm as a mechanism underlying telomere and telomerase activity control that serve as interconnections between circadian systems and aging.     

Analysis of trough and peak of plasma melatonin circadian rhythm in ewes

This study evaluates the pattern of plasma melatonin during the trough and the peak of its daily rhythm. Blood samples from 8 ewes were collected every 3 h for a 48-h period. On the third day, blood samples were collected from 10:00 to 13:00 (trough) and from 20:00 to 23:00 (peak) every 20 min. Our results showed a robust daily rhythm of melatonin in both days of monitoring, with nocturnal acrophase. During the trough, a significant decrease was observed starting from the 10:40 with a progressive decrease about every 40 min. During the peak of the plasma melatonin daily rhythm, an increase was observed starting from the 20:40 with a progressive increase about every 40 min. These data could be taken in consideration to monitor the plasma melatonin variations during the 24 h, and for the administration of melatonin for breeding in ewes.     

Case study of circadian rhythm sleep disorder following haloperidol treatment: reversal by risperidone and melatonin

A patient with Gilles de la Tourette syndrome treated with haloperidol, ingested once daily after awakening from sleep, exhibited an irregular sleep-wake pattern with a free-running component of approximately 48 h. Transfer to risperidone, ingested once daily after awakening from sleep, was beneficial resulting in a sleep-wake cycle more synchronized at the appropriate phase to the external zeitgebers, and fewer nocturnal disturbances. The circadian sleep-wake schedule was fully synchronized when the patient had been subsequently treated with melatonin at 21:00h, before intended nocturnal sleep, in addition to risperidone in the morning. Restoration of the sleep-wake circadian pattern was accompanied by the patient's subjective report of significant improvement in his quality of life, social interactions, and occupational status. This observation suggests that circadian rhythm sleep disorders can be related to the typical neuroleptic haloperidol and restored by the atypical neuroleptic risperidone. Similar findings reported in patients suffering from other disorders support the hypothesis that the described disruption of the sleep-wake schedule is medication rather than illness-related. Therefore, it is very important to realize that circadian rhythm sleep disorders may be a side effect of neuroleptics.     

Melatonin modulates the ERG circadian rhythm in crayfish

One of the most important functions modulated by melatonin is the synchronization of circadian rhythms. In crayfish (Procambarus clarkii), we have obtained evidence that the amplitude of the electrical response to light of the retinal photoreceptors the receptor potential, is modified by the action of melatonin and that the magnitude of this action depends on the circadian time of melatonin application. In contrast, the electroretinogram (ERG) circadian rhythm can be synchronized by either single or periodic melatonin application. In this work we hypothesized that, in crayfish, melatonin acts on effectors and on pacemaker of ERG circadian rhythm as a non-photic synchronizer. Melatonin could be a hormone that sends a signal of darkness to the ERG circadian system.     

A rapid circadian rhythm of carbon-dioxide metabolism in Bryophyllum fedtschenkoi

Leaves of Bryophyllum fedtschenkoi Hamet et Perrier maintained in a stream of normal air and at 15° C exhibit a circadian rhythm of CO₂ uptake in continuous light but not in continuous darkness. The rhythm is unusual in that it persists for at least 10 d, and has a short period of approximately 18 h. The mechanism by which this rhythm is generated is discussed.Abbreviation PEPCase phosphoenolpyruvate carboxylase     

In-vitro circadian rhythm of murine bone marrow progenitor production

Hematopoietic processes display 24h rhythms both in rodents and in human beings. We hypothesized these rhythms to be in part generated by a circadian oscillator within the bone marrow. The ability of murine bone marrow granulo-monocytic (GM) precursors to form colonies following colony-stimulating factor (rm GM-CSF) exposure was investigated in liquid culture samples obtained every 3 h for a span of up to 198 h. The CFU-GM count varied rhythmically over the first 4 d of culture, with a reproducible maximum in the early morning hours, similar to that observed in vivo. These experiments provide the first evidence that bone marrow progenitors sustain in vitro circadian rhythmicity, and they demonstrate the presence of a circadian time-keeping system within these cells. The results support the potential usefulness of bone marrow cultures for investigating chronopharmacologic effects of anticancer drugs and cytokines on this target system.     

The circadian rhythm of core temperature: origin and some implications for exercise performance

This review first examines reliable and convenient ways of measuring core temperature for studying the circadian rhythm, concluding that measurements of rectal and gut temperature fulfil these requirements, but that insulated axilla temperature does not. The origin of the circadian rhythm of core temperature is mainly due to circadian changes in the rate of loss of heat through the extremities, mediated by vasodilatation of the cutaneous vasculature. Difficulties arise when the rhythm of core temperature is used as a marker of the body clock, since it is also affected by the sleep-wake cycle. This masking effect can be overcome directly by constant routines and indirectly by “purification” methods, several of which are described. Evidence supports the value of purification methods to act as a substitute when constant routines cannot be performed. Since many of the mechanisms that rise to the circadian rhythm of core temperature are the same as those that occur during thermoregulation in exercise, there is an interaction between the two. This interaction is manifest in the initial response to spontaneous activity and to mild exercise, body temperature rising more quickly and thermoregulatory reflexes being recruited less quickly around the trough and rising phase of the resting temperature rhythm, in comparison with the peak and falling phase. There are also implications for athletes, who need to exercise maximally and with minimal risk of muscle injury or heat exhaustion in a variety of ambient temperatures and at different times of the day. Understanding the circadian rhythm of core temperature may reduce potential hazards due to the time of day when exercise is performed.     

Modeling the circadian variability of ambulatorily monitored blood pressure by multiple-component analysis

The use of a set of new end points derived from ambulatory blood pressure monitoring (ABPM), in addition to the blood pressure (BP) values themselves, has been advocated to improve the sensitivity and specificity in diagnosing hypertension and to evaluate a person's response to treatment. An adequate estimation of rhythmic parameters depends, however, on the ability to describe properly the circadian pattern of BP variability. The purpose of this study was to identify a simple model that could characterize sufficiently well the circadian pattern of BP in normotensive healthy volunteers sampled by ambulatory monitoring. We studied 278 clinically healthy Spanish adults (184 men), 22.7±3.3 yr of age, without medical history of hypertension and mean BP from ambulatory profiles always below 135/85 mmHg for systolic/diastolic BP, who underwent sequential ABPM providing a total of 1115 series of BPs and heart rates (HRs), sampled on each occasion at 0.5h intervals for 48 h. Subjects were assessed while adhering to their usual diurnal activity and nocturnal sleep routine, without restrictions but avoiding the use of medication. The circadian rhythm in BP and HR for each subject was established by multiple-component analysis. A statistically significant 24h component is documented for 97% of the BP profiles, with a significant second (12h) harmonic documented in 65% of the profiles. Other ultradian harmonic components were significant in less than 20% of the profiles. A statistically significant increase in the coefficient of determination (percent of overall variability explained by the function fitted to the data) was only obtained after including the periods of 24 and 12 h for BP, and periods of 24, 12, and 6 h for HR in the model components. Although other ultradian components can be demonstrated as statistically significant in a small percent of subjects, a rather simple model including only the two first harmonics of the 24h period describes sufficiently well, at the specified sampling rate, the circadian pattern of BP in normotensive subjects. Departure from this model could characterize overt pathology, as recently demonstrated in the diagnosis of preeclampsia.     

Modeling the circadian variability of ambulatorily monitored blood pressure by multiple-component analysis

The use of a set of new end points derived from ambulatory blood pressure monitoring (ABPM), in addition to the blood pressure (BP) values themselves, has been advocated to improve the sensitivity and specificity in diagnosing hypertension and to evaluate a person's response to treatment. An adequate estimation of rhythmic parameters depends, however, on the ability to describe properly the circadian pattern of BP variability. The purpose of this study was to identify a simple model that could characterize sufficiently well the circadian pattern of BP in normotensive healthy volunteers sampled by ambulatory monitoring. We studied 278 clinically healthy Spanish adults (184 men), 22.7±3.3 yr of age, without medical history of hypertension and mean BP from ambulatory profiles always below 135/85 mmHg for systolic/diastolic BP, who underwent sequential ABPM providing a total of 1115 series of BPs and heart rates (HRs), sampled on each occasion at 0.5h intervals for 48 h. Subjects were assessed while adhering to their usual diurnal activity and nocturnal sleep routine, without restrictions but avoiding the use of medication. The circadian rhythm in BP and HR for each subject was established by multiple-component analysis. A statistically significant 24h component is documented for 97% of the BP profiles, with a significant second (12h) harmonic documented in 65% of the profiles. Other ultradian harmonic components were significant in less than 20% of the profiles. A statistically significant increase in the coefficient of determination (percent of overall variability explained by the function fitted to the data) was only obtained after including the periods of 24 and 12 h for BP, and periods of 24, 12, and 6 h for HR in the model components. Although other ultradian components can be demonstrated as statistically significant in a small percent of subjects, a rather simple model including only the two first harmonics of the 24h period describes sufficiently well, at the specified sampling rate, the circadian pattern of BP in normotensive subjects. Departure from this model could characterize overt pathology, as recently demonstrated in the diagnosis of preeclampsia.     

No endogenous circadian rhythm in resting plasma Hsp72 concentration in humans

Extra-cellular (e) heat shock protein (Hsp)72 has been shown to be elevated in a number of clinical conditions and has been proposed as a potential diagnostic marker. From a methodological and diagnostic perspective, it is important to investigate if concentrations of eHsp72 fluctuate throughout the day; hence, the purpose of the study was to measure resting concentrations of plasma eHsp72 throughout a 24-h period. Blood samples were taken every hour from 1200-2100 hours and from 0700-1200 hours the following day from seven healthy recreationally active males. Participants remained in the laboratory throughout the trial, performed light sedentary activities and were provided with standardised meals and fluids. Physical activity was quantified throughout by the use of an accelerometer. Ethylenediaminetetraacetic acid blood samples were analysed for eHsp72 concentration using a commercially available high-sensitivity enzyme-linked immunosorbent assay (intra-assay coefficient of variation = 1.4%). One-way repeated measures analysis of variance revealed that measures of physiological stress such as heart rate, systolic and diastolic blood pressure remained stable throughout the trial and subjects remained sedentary throughout (mean activity energy expenditure above resting metabolic rate-35.7 +/- 10.0 kcalh(-1)). Plasma Hsp72 concentration did not fluctuate significantly throughout the day and showed no apparent endogenous circadian rhythm in absolute (P = 0.367) or plasma volume change corrected data (P = 0.380). Individual coefficients of variation ranged from 3.8-7.7% (mean 5.4%). Mean Hsp72 concentration across all subjects and time points was 1.49 +/- 0.08 ngml(-1). These data show that in a rested state, plasma eHsp72 concentration shows no apparent endogenous circadian rhythm.     

Geographical and species variation in circadian rhythm parameters in nemobiine crickets

Abstract. . Locomotor activity rhythms were studied in eight species of nemobiine crickets with different habitat preferences. They showed similar patterns with a major peak of activity around dusk and a minor one around dawn. These patterns did not change within the natural range of daylengm (12–16 h). The acrophase time of the rhythm varied between -3.2 and +3.5 h as measured from dusk, and the free-running period (T) varied between 22.8 and 24.5 h. In the Dianemobius fascipes species complex these circadian parameters varied among nine local strains (8^oS to 43^oN) but did not show any latitudinal trend. In a temperate strain of this species complex (Dianemobius nigrofasciatus from Teshikaga, 43^oN), two lines which differed from each other in mean T by 1.4h were selected, and a high heritability of T, 0.78 + 0.20 (mean±SE) was obtained. On the other hand, in a subtropical strain (Dianemobius fascipes from Ishigaki Island, 24^oN), low heritabilities, 0.35 ± 0.15 for acrophase and 0.17 ± 0.21 for T, were obtained from the full-sib correlations. The variation in i seemed to be random and not related to fitness.     

Plasma hyaluronan concentration: no circadian rhythm but large effect of food intake in humans

This study was designed to determine if a circadian rhythm in plasma hyaluronan concentration [HA] exists in the absence of physical activity, and if plasma [HA] is associated with feeding in human subjects. Five persons were studied under standardized conditions, blood samples being taken between 0600 and 2200 hours at 30-min intervals. Any orthostatic challenge and muscle activity was abolished by immobilization by a 6° head-down bed-rest, and the effect of a quasi-continuous ingestion of energy compared a normal, three-portion diet of equivalent energy content or to fasting. Reproducibility of HA profiles on two consecutive half-days was also studied. A highly sensitive immunoassay was used to determine plasma [HA]. The data indicated that without physical activity and without food ingestion, [HA] was unchanged and displayed no diurnal rhythm. In addition, we observed that [HA] increased after the first food intake, peaking after 60 min, and concluded from our results that without ingestion of a larger meal, and sessions of postural or muscle activity, no circadian plasma [HA] rhythm exists. Accepted: 10 June 1998     

The semidian rhythm in flowering response of Pharbitis nil in relation to dark period time measurement and to a circadian rhythm

When seedlings of Pharbitis nil Choisy, cv. Violet, are exposed to a single inductive dark period at 27°C, brief interruptions with red light (R) can be promotive after 2–3 h of darkness but increasingly inhibitory to flowering up to the 8–9th h of darkness. This rhythmic response to R interruptions can be advanced in phase by > 1 h when the preceding light period is interrupted with far-red (FR) 2 h before darkness (FR -2 h) or with FR – 15 h, whereas FR –8 h or FR–22 h retard the rhythm. These shifts in the R interruption rhythm are paralleled by equal shifts in the length of the dark period required for flowering. Brief FR interruptions of darkness displayed a similar rhythm which was also advanced by FR –2 h and retarded by FR –8 h. We conclude therefore that the semidian rhythm in the light, which we have previously described, continues through at least the first 12 h of darkness, is manifested in the R interruption rhythm, and determines the critical night length. A circadian rhythm with a marked effect on flowering was also identified, but several lines of evidence suggest that the circadian and semidian rhythms have independent additive effects on flowering and do not appear to show phase interaction.     

Comparison of the circadian eclosion rhythm between non-diapause and diapause pupae in the onion fly,Delia antiqua

The influence of pupal diapause on adult eclosion rhythm of Delia antiqua was investigated. When non-diapause and diapause pupae were exposed to various photoperiods at 15, 20 and 25 °C, both of them emerged as adults close to the light-on time, but the phase of eclosion varied with photoperiod and temperature. Moreover, there was a significant difference in the eclosion time between non-diapause and diapause pupae; the eclosion peak of diapause pupae was earlier than that of non-diapause pupae. When non-diapause and diapause pupae were transferred to constant darkness (DD) after having experienced LD 12:12 at 15, 20 and 25 °C, both showed circadian rhythmicity in eclosion. Although the free-running period (τ) decreased slightly as temperature increased in both non-diapause and diapause pupae, the latter tended to show shorter τ than the former. This observation suggests that the observed difference in eclosion time in LD cycles between non-diapause and diapause pupae is due to differences in τ.     

Evidence of circadian rhythm of electric discharge in Eigenmannia virescens system

The gymnotid electric fish, Eigenmannia virescens, exhibits electric discharge rhythmicity both in alternate light-dark (LD; 12h light, 12h dark [LD 12:12]) and in constant dark (DD) conditions. It suggests that the electric discharge rhythm is under control of the circadian clock. The free-running periods (FRPs) of electric discharge rhythms at 21°C in DD are greater than, but close to, 24h. The maximum of the electric discharge in the Eigenmannia system peaks approximately at circadian time 6 (CT6) in the middle of the subjective day. The circadian oscillator in the system is temperature compensated. This original report reveals the relationship between electric discharge activity and the circadian pacemaker in Eigenmannia and provides an alternative system to investigate circadian rhythms in vertebrates. (Chronobiology International, 17(1), 43-48, 2000)     

Effects of melatonin and antagonists of MT1 and MT2 receptors on somatic pain induced within the fixed circadian rhythm

We studied behavioral pain-related reactions (PRRs) induced in mice by subcutaneous injections of 5% formalin within different phases of the fixed circadian illumination rhythm under conditions of administration of exogenous melatonin and of blocking of MT1 and MT2 melatonin receptors. It was demonstrated that modulation of experimentally induced somatic pain depends considerably on the phase of the preset circadian rhythm. In the norm, the duration of PRRs in the middle of the dark phase was 30% smaller than that in the middle of the light phase. Administration of exogenous melatonin in the middle of the light phase decreased the duration of episodes of noxious behavior by 43%, on average. Injections of melatonin within the dark phase resulted in no significant changes in the duration of PRRs. In the dark phase, the blockade of MT1 receptors by luzindole led to an increase in the duration of PRRs by 45%, as compared with the norm, while in the light phase we observed no significant alterations of this duration under conditions of blocking of the above-mentioned receptors. The blockade of MT2 receptors by prazocine in the middle of dark and light phases increased the durations of PRRs by 92 and 28%, respectively. Our data indicate that the analgesic effect of melatonin depends significantly on the level of this hormone in the organism; in turn, such a level is determined by the illumination conditions. The antinoxious effect of melatonin is mediated by MT receptors, in particular by MT2 receptors. Neirofiziologiya/Neurophysiology, Vol. 39, No. 3, pp. 255–259, May–June, 2007.     

A note on the circadian rhythm and feeding behaviour of sheep fitted with a lightweight GPS collar

The circadian rhythm and feeding behaviour (bite rate) of 16 Scottish Blackface ewes of which eight were fitted with a lightweight (863 g) GPS collar were examined. The collar consisted of a leather harness and a 0.5 l aluminium box and represented 2.2% of the average body mass of the study ewes. No differences in circadian rhythm and bite rate were found between ewes fitted with the collars and ewes that were not. The relevance of using collar weight as a proportion of body mass as a guide to gauge its impact on the feeding behaviour of small ruminant (35–75 kg) herbivores is questioned.