PRESENCE OF CIRCADIAN RHYTHMS IN THE LOCOMOTOR ACTIVITY OF A CAVE-DWELLING MILLIPEDE GLYPHIULUS CAVERNICOLUS SULU (CAMBALIDAE,SPIROSTREPTIDA)

The locomotor activity of the millipede Glyphiulus cavernicolus (Spirostreptida), which occupies the deeper recesses of a cave, was monitored in light-dark (LD) cycles (12h light and 12h darkness), constant darkness (DD), and constant light (LL) conditions. These millipedes live inside the cave and are apparently never exposed to any periodic factors of the environment such as light-dark, temperature, and humidity cycles. The activity of a considerable fraction of these millipedes was found to show circadian rhythm, which entrained to a 12:12 LD cycle with maximum activity during the dark phase of the LD cycle. Under constant darkness (DD), 56.5% of the millipedes (n = 23) showed circadian rhythms, with average free-running period of 25.7h ± 3.3h (mean ± SD, range 22.3h to 35.0h). The remaining 43.5% of the millipedes, however, did not show any clear-cut rhythm. Under DD conditions following an exposure to LD cycles, 66.7% (n = 9) showed faint circadian rhythm, with average free-running period of 24.0h ± 0.8h (mean ± SD, range 22.9h to 25.2h). Under constant light (LL) conditions, only 2 millipedes of 11 showed free-running rhythms, with average period length of 33.3h ± 1.3h. The results suggest that these cave-dwelling millipedes still possess the capacity to measure time and respond to light and dark situations. (Chronobiology International, 17(6), 757–765, 2000)     

Different circadian pacemakers control feeding and locomotor activity rhythms in European starlings

Summary In higher organisms, many physiological and behavioral functions exhibit daily variations, generated by endogenous circadian oscillators. It is not yet clear whether all the various rhythms that occur within an individual depend on one and the same pacemaker or whether different pacemakers are involved. To examine this question, the feeding and perch-hopping rhythms were measured in European starlings (Sturnus vulgaris) under light-dark cycles and continuous dim light. In dim light, the internal phase relationship between the feeding and perch-hopping rhythms changed systematically as a function of the circadian period, and the two rhythms could even dissociate and show different circadian periods in individuals with extremely long or extremely short circadian periods. Moreover, in some birds kept on lowamplitude light-dark cycles, the rhythm of feeding was synchronized 180° out of phase with the rhythm of locomotor activity. These results strongly suggest that in the European starling the feeding and locomotor activity rhythms are controlled by separate circadian pacemakers.     

Feeding entrainment of locomotor activity rhythms in the goldfish is mediated by a feeding-entrainable circadian oscillator

Periodic food availability can act as a potent zeitgeber capable of synchronizing many biological rhythms in fishes, including locomotor activity rhythms. In the present paper we investigated entrainment of locomotor rhythms to scheduled feeding under different light and feeding regimes. In experiment 1, fish were exposed to a 12:12?h light/dark cycle and fed one single daily meal in the middle of the light phase. In experiment 2, we tested the effect of random versus scheduled feeding on the daily distribution of activity. During random feeding, meals were randomly scheduled with intervals ranging from 12 to 36?h, while scheduled feeding consisted of one single daily meal set in the middle of the light or dark phase. Finally, in experiment 3, we studied the synchronization of activity rhythms to feeding under constant darkness (DD) and after shifting the feeding cycle by either advancing or delaying the feeding cycle by 9?h. The results revealed that goldfish synchronized to feeding, overcame light entrainment and significantly changed their daily distribution of activity according to their feeding schedule. In addition, the daily activity pattern modulated by feeding differed between layers: a peak of activity being noticeable directly after feeding at the bottom, while an anticipatory behaviour was obvious at the surface of the tank. Under DD and no food, free-running rhythms averaging 25.5?± 1.9?h (mean?±?SD) were detected. In conclusion, some properties of feeding entrainment (e.g. anticipation of the feeding time, free-running rhythms following termination of periodic feeding, and the stability of ø after shifting the feeding cycle) suggested that goldfish have (a) separate but tightly coupled light- and food-entrainable oscillators, or (b) a single oscillator that is entrainable by both light and food (one synchronizer being eventually stronger than the other).     

Seasonality of circadian locomotor activity in an insect

Daily periodic locomotor activity of Carabus auronitens was recorded in a climate-constant laboratory with the animals exposed to naturally changing photoperiods. Most actograms exhibit directed seasonal variations of duration and phase position of daily activity. Seasonal locomotor activity starts in early spring (following dormancy) on a low daily level, first being confined to a short time span around dusk (and even shorter around dawn). In the course of season, the daily onsets of activity become closely related with sunset and the duration of daily activity is steadily extended with both parts of the bimodal phase fusing to a common, unimodal activity band by late spring. Subsequently, it is further extended into forenoon, until in summer (shortly before aestivation), spontaneous phase inversion turns activity periodicity from nocturnality into diurnality within 1 day. Such seasonal variations are paralleled by changes in the precision of synchronization of the individuals' activity rhythms to the entraining light/dark cycle. No geographical differences were detected. The results support the idea of the circadian clock as a system of two dynamically coupled physiological oscillators that invert their phase relation as soon as the natural dark phase falls short of some minimum-tolerable night length.Abbreviations LD light/dark cycle - nLD natural light/dark cycle - DD constant darkness - endogenous period length - SS sunset - SR sunrise - PRC phase-response curve     

Effects of dark-light step transitions on circadian locomotor activity rhythms of the hagfish,Eptatretus burgeri

Captive hagfish,Eptatretus burgeri, were subjected to step transitions from continuous dark (DD) to continuous light (LL) and their locomotor activity patterns recorded. Free-running activity rhythms occurred in both the DD and LL regimes. The timing of the transition influenced the circadian period (τ), the relationship between the period response (δτ, or τ{inLL}–τ{inDD}, change in the circadian period) and the former being represented by a cosine curve δτ became most positive and most negative when hagfish underwent a DD-LL transition shortly before the beginning of the duration of activity (α) and shortly after the end of such, respectively. The phase response (δ-phase, change in the relative timing of the activity phase) was characterized by a delay in the activity phase after the DD-LL transition, although its magnitude bore no relation to the timing of the transition.     

Interseasonal variation in the circadian rhythms of locomotor activity and temperature selection in sleepy lizards, <Emphasis Type="Italic">Tiliqua rugosa</Emphasis>

Few studies in non-mammalian vertebrates have examined how various effectors of the circadian system interact. To determine if the daily locomotor and behavioural thermoregulatory rhythms of Tiliqua rugosa are both controlled by the circadian system in different seasons, lizards were tested in laboratory thermal gradients in four seasons and in constant darkness. Circadian rhythmicity for both rhythms was present in each season, being most pronounced in spring and summer and least evident in autumn. Most lizards displayed a unimodal locomotor activity pattern across all seasons. However, some individuals presented a bimodal locomotor activity pattern in spring and summer. Seasonal variations in the phase relationships of both rhythms to the light:dark (LD) cycle were demonstrated. No seasonal differences in the free-running period lengths of either rhythm were detected, raising the possibility that a single circadian pacemaker drives both rhythms in this species. Our present results demonstrate that both rhythms are similarly controlled by the circadian system in each season. Although seasonal variations in the thermal preferences of reptiles both in the field and laboratory have previously been well documented, this study is the first to demonstrate circadian rhythms of temperature selection in a reptile species in each season.     

Daily and circadian rhythms of locomotor activity in the American lobster, Homarus americanus

It is widely accepted that American lobsters, Homarus americanus (Milne-Edwards), are nocturnally active. However, the degree to which this rhythm is expressed by different individuals and the underlying causes of lobster activity rhythms, are poorly understood. In order to address these issues we recorded daily patterns of lobster locomotion using two novel techniques. In the first, reed switch assemblies were used to monitor the distance traveled by freely moving lobsters (n=43), each fitted with a small magnet, as they walked around a 1 m diameter racetrack. The advantages of this technique included: (1) lobsters were freely moving; (2) the system could be deployed in laboratory tanks or in the field and; (3) actual distances moved were measured, not just relative activity. The second technique involved placing individual lobsters (n=10) into custom-designed running wheels. This allowed for continuous monitoring of locomotor activity for extended durations (>45 days) under normal light/dark (L/D) cycles, as well as in constant darkness (D/D) and constant light (L/L).Under ambient light conditions lobsters in the racetracks moved an average of 60.1±6.5 m/day in flow-through seawater tanks. Overall, lobsters were significantly more active at night, moving 4.1±0.4 m/h in the dark vs. 1.0±0.2 m/h in the light. However, many of the lobsters moved as much during the day as during the night.Lobsters in the running wheels moved an average of 36.6±11.7 m/day and 80% expressed clear daily rhythms of activity, with a mean periodicity of 24.0±0.1 h under L/D conditions. Under D/D conditions 90% of the animals expressed free-running circadian rhythms with a mean periodicity of 24.2±0.3 h, indicating that this species possesses endogenous rhythmicity. While the running wheel results show that the nocturnal pattern of locomotor activity for this species is strongly influenced by an endogenous circadian clock, the results from the racetracks show that there is remarkable variability in the extent to which they express this pattern under natural conditions.     

Exogenous corticosteroid and shifts of circadian rhythms in hamsters

We tested the hypothesis that glucocorticoid stimulation mediates the effect of exercise on circadian clock resetting in hamsters. We injected animals with 1 and 5 mg dexamethasone—a potent glucocorticoid agonist—at zeitgeber time (ZT) 4 and ZT6, circadian phases at which vigorous exercise induces maximal phase advances of about 3h. Neither dose of dexamethasone induced phase shifts that were significantly larger than those induced by injections of saline vehicle at either of the phases tested. Some animals, however, showed quite large and consistent phase shifts to repeated injections whether with saline or dexamethasone, such that there was a statistically significant correlation between individuals' responses to the two treatments. The data indicate no role for increased glucocorticoid activity in mediating the effects of exercise on circadian phase shifting, but suggest a modest role for nonspecific stimulation, independent of exercise, in inducing phase shifts at ZT4-ZT6. (Chronobiology International, 18(2), 203-213, 2001)     

Pharmacological effects of vinorelbine on body temperature and locomotor activity circadian rhythms in mice

The effects of vinorelbine (VRL) on the circadian rhythms in body temperature and locomotor activity were investigated in unrestrained B6D2F₁ mice implanted with radio-telemetry transmitters. A single intravenous VRL dose (24 or 12 mg/kg) was given at 7 h after light onset (HALO), a time of high VRL toxicity, and resulted in transient suppression of temperature and activity circadian rhythms in mice kept in light-dark (LD) 12h:12h. Such suppression was dose-dependent. It occurred within 1-5 d after VRL dosing. Recovery of both rhythms was partially complete within 5 d following the high dose and within 2 or 3 d after the low dose and was not influenced by suppression of photoperiodic synchronization by housing in continuous darkness. Moreover, VRL induced a dose-dependent relative decrease in amplitude and phase shift of the temperature circadian rhythm. The mesor and amplitude of the activity rhythm were markedly reduced following the VRL administration. The relevance of VRL dosing time was studied in mice housed in LD 12h:12h. Vinorelbine was injected weekly (20 mg/kg/injection) for 3 wk at 6 or 18 HALO. Vinorelbine treatment ablated the rest-activity and temperature rhythms 3-6 d after each dose, with fewer alterations after VRL dosing at 18 HALO compared to 6 HALO, especially for the body temperature rhythm. There was at least partial recovery 1 wk after dosing, suggesting the weekly schedule of drug treatment is acceptable for therapeutic purposes. Our findings demonstrate that VRL can transiently, yet profoundly, alter circadian clock function. Vinorelbine-induced circadian dysfunction may contribute to the toxicokinetics of this and possibly other anticancer drugs.     

Modelling circadian rhythms of protein KaiA, KaiB and KaiC interactions in cyanobacteria

Cyanobacteria are the simplest organisms known that exhibit circadian rhythms. The mechanism of circadian rhythm generation in cyanobacteria is different from eukaryotes. Based on the recent experiments about the interaction of KaiA, KaiB, and KaiC proteins with the generation of circadian rhythms in vitro, we developed a mathematical model to describe post-translational oscillations and the possible chemical reactions involved in the circadian clock mechanism of cyanobacteria. In this model, a series of differential equations, with linear kinetics for binding of proteins, Michaelis - Menten kinetics for enzymatic processes and a term including an explicit delay for dissociation of the KaiA/KaiB/phospho-KaiC complex, are proposed describing the dynamics of the chemistry. It is demonstrated that the mathematical system can lead to circadian oscillation within a range of parameter values.     

Sleep and circadian rhythms: key components in the regulation of energy metabolism

In this review, we present evidence from human and animal studies to evaluate the hypothesis that sleep and circadian rhythms have direct impacts on energy metabolism, and represent important mechanisms underlying the major health epidemics of obesity and diabetes. The first part of this review will focus on studies that support the idea that sleep loss and obesity are "interacting epidemics." The second part will discuss recent evidence that the circadian clock system plays a fundamental role in energy metabolism at both the behavioral and molecular levels. These lines of research must be seen as in their infancy, but nevertheless, have provided a conceptual and experimental framework that potentially has great importance for understanding metabolic health and disease.     

Endogenous cardiac activity rhythms of continental slope Nephrops norvegicus (decapoda: nephropidae)

The endogenous cardiac activity rhythm of the Norway lobster Nephrops norvegicus was studied under constant conditions of darkness by means of a computer-aided monitoring system (CAPMON). Time series recordings of the heart rate (beats min^-1) were obtained from 47 adult males freshly collected from the continental slope (400-430 m) in the western Mediterranean. Periodogram analysis revealed the occurrence of circadian periodicity (of around 24 h) in most cases. A large percentage of animals showed significant ultradian periods (of around 12 and 18 h). The analysis of the circadian time series revealed the occurrence of peaks of heart rate activity during the expected night phase of the cycle. These results are discussed in relation to the emergence and locomotor activity rhythms of the species.     

Complete suprachiasmatic lesions eliminate circadian rhythmicity of body temperature and locomotor activity in golden hamsters

The effects of suprachiasmatic and control lesions on the circadian rhythms of locomotor activity and body temperature were studied in golden hamsters (Mesocricetus auratus) maintained in constant light as well as constant darkness. Large suprachiasmatic lesions, but not control lesions, eliminated circadian rhythmicity in locomotor activity as well as in body temperature. Analysis of the robustness of the rhythms of locomotor activity and body temperature in unlesioned and lesioned animals suggests that, because body temperature rhythmicity is more robust than locomotor rhythmicity, lesions that spare a small number of suprachiasmatic cells might abolish the latter but not the former. Our results do not support the hypothesis that the body temperature rhythm is controlled by a circadian pacemaker distinct from the main pacemaker located in the suprachiasmatic nuclei.     

Role of the microbiota in circadian rhythms of the host

ABSTRACT

Life for meta-organisms is based on a strong relationship between gut bacteria and body cells. This review summarizes to what extent the microbiota can influence host circadian rhythms via a literature review on the topic. The results show that microbiota can influence the host’s circadian gene expression through direct interactions via immunoreceptors and microbiota-derived metabolites, especially in peripheral tissues. Noteworthy metabolites that are only attributable to the microbiota are short-chain fatty acids and unconjugated bile acids. The microbiota also serves as a mediator for the interplay between the host’s diet and circadian rhythmicity. This work furthermore displays that the microbiota is subject to diurnal variations in terms of structure and function and that the host and the host’s diet influence these fluctuations. As most of these results originate in mouse models, we hope this work stimulates further research in human derived tissue to verify these conclusions.     

Effects of suprachiasmatic nuclei lesions on circadian and ultradian rhythms in body temperature in ocular enucleated rats

Abstract

To test the hypothesis that an oscillator located outside the suprachiasmatic nuclei (SCN) controls the circadian rhythm of body temperature, we conducted a study with 14 blinded rats, 10 of which receiving a SCN lesion. Body temperature was automatically and continuously recorded for about one month by intraperitoneal radio transmitters. Food intake, drinking and locomotor activity were also recorded. Periodograms revealed that 3 rats with histologically verified total bilateral SCN lesions did not exhibit any circadian rhythmicity. The 7 other rats appeared to have partial lesions. They showed shortening of period and severe amplitude reduction in all functions. Thus, no support was found for the hypothesis of a separate circadian ‘temperature oscillator’ located outside the SCN. Nevertheless, after large partial lesions body temperature showed more persistency than some of the other behavioral rhythms.

Ultradian rhythms in temperature persisted after partial and total lesions. Other functions showed parallel ultradian rhythms. In intact rats the ultradian peaks were restricted predominantly to the subjective night. After total lesions these peaks became more or less homogeneously distributed in time but more heterogeneously after partial lesions. So the SCN plays a role in the temporal structure of ultradian rhythms but does not generate them. Non‐24‐hour actograms showed instabilities of period and phase of ultradian rhythms. Intact and lesioned rats were similar with respect to the mean (about 3.5 hrs) and standard deviation (about 1.5 hrs) of ultradian periods in temperature. These features indicate that a mechanism outside the SCN is underlying ultradian rhythmicity, capable of generating short‐term oscillations. Two approaches, homeostatic sleep‐wake relaxation oscillations and multiple circadian oscillators, are discussed.     

Effects of a seven-day continuous infusion of ropivacaine on circadian rhythms in the rat

The present study was conducted to evaluate the effect of a 7 d continuous infusion of ropivacaine on the 24 h rhythms of body temperature, heart rate, and locomotor activity. After an initial 7 d baseline, rats were randomly divided into two groups of 4 rats each to receive ropivacaine or saline via an osmotic pump for 7 consecutive days. The pumps were removed thereafter and observed during a 7 d recovery span. The studied circadian rhythms were measured by radiotelemetry throughout each of the 7 d periods. An additional group of 4 rats was studied under the same experimental conditions to assess the plasma levels of ropivacaine on days 3 and 8 following pump implantation. Our results indicate that ropivacaine does not induce loss of the circadian rhythms of body temperature, heart rate, or locomotor activity; a prominent period of 24 h was found for all variables in all animals, before, during, and after ropivacaine treatment. However, ropivacaine treatment did modify some characteristics of the rhythms; it increased the MESOR (24 h mean) of the heart rate and locomotor activity rhythms and advanced the acrophase (peak time) of the locomotor activity circadian rhythm. The present study indicates that the circadian rhythms of heart rate and locomotor activity are modified after continuous infusion of ropivacaine, which is of particular interest, given the potential cardiotoxicity of this local anesthetic agent.     

The role of the pineal and the retinae in the expression of circadian locomotor rhythmicity in the ruin lizard,Podarcis sicula

Summary A marked interspecific variability in the role played by the pineal and the retinae characterizes the circadian system of lizards. I examined the role played by these structures in a new model species, the ruin lizard, Podarcis sicula. In constant temperature and darkness pinealectomy as well as bilateral removal of the retinae produced significant changes (both lengthening and shortening) in the freerunning period of locomotor rhythms. Circadian activity time was also affected by pinealectomy. Circadian locomotor rhythmicity persisted in all cases even when both operations were combined in the same individuals. This demonstrates in Podarcis sicula the existence of an oscillatory system outside the pineal and the retinae which can drive locomotor rhythms. The period changes recorded after pinealectomy as well as after bilateral removal of the retinae specifically suggest that both the pineal and the retinae play a modulating role on circadian oscillators located elsewhere in the system, with the final effect of stabilizing the overt rhythms.Abbreviations DD constant darkness - LL constant light - PIN-X pinealectomy - RET-X bilateral removal of the retinae - SHAM sham pinealectomy - circadian activity time - freerunning circadian period