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.     

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.     

Temperature and light effects on the circadian rhythm and locomotory activity of the plains garter snake (Thamnophis radix hayendi)

Abstract

The Locomotory activity of the Plains Garter snake was determined under L/D: 12/12 conditions at five constant temperatures and three light intensities during the light period. The snakes were diurnal at low temperatures with nocturnal activity increasing in various amounts at higher temperatures. The different light intensities had relatively small effects on the activity rhythm.

Activity was recorded under four constant light conditions at five constant temperatures and the characteristics of the free‐running rhythm measured. A comparison of the characteristics of the free‐running rhythm to Aschoff's circadian rule indicates that this snake is an exception to this rule.

Increase light intensity decreased total activity under all conditions. Under a L/D: 12/12 cycle the decrease in activity was more pronounced during the dark period than the light period.

It is suggested that crepuscular or nocturnal activity shown by snakes at high temperatures may be an effect the temperature level has on the biological clock and activity controlling mechanisms rather than temperature selection by the snake.     

Contrast in the circadian behaviors of an electrodermal activity and bioimpedance spectroscopy

ABSTRACT

Probing the electrical response of the human body is minimally invasive and a promising area of investigation for future health care. The electrical responses of individuals may vary depending on daily physiological rhythms or environmental changes, which may hamper their prediction for pathological status. In this study, we observed circadian expressions via both alternating current (AC) and direct current (DC) electrical responses of the human body using bioelectrical impedance analysis (BIA) and electrodermal activity (EDA). In total, 14 healthy adults (9 males and 5 females) participated and were hospitalized for 2 nights with controlled caloric intake, sleep hours and residential conditions. The EDA data showed a significant circadian rhythm, but the BIA data did not show significant modulations during the measurement period. No difference was found between circadian changes in male and female participants. The acrophase of the EDA voltage response showed similar behavior with variations in the heart rate variability, with a resistance minimum occurring at approximately 4 pm, implying that the behavior of the EDA is probably affected by the sympathetic nerve response. Moreover, the resistance of the EDA varied by up to 15% from its mean value, which suggests that circadian variations cannot be neglected for the correct diagnosis of pathological conditions. In contrast, the BIA method did not show this circadian variation but showed independent results over the measurement period. This difference in performance implies that the DC and AC responses of the human body contain different electrophysiological information.     

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.     

Food ingestion and circadian rhythmicity

Feeding is organised within the 24-h of the light - dark (LD) cycle. Food is ingested in a circadian manner in nature and in laboratory animals kept under constant conditions. The circadian rhythmicity in food ingestion is driven by a biological clock located in the suprachiasmatic nuclei (SCN) of the hypothalamus. The circadian organisation of food ingestion not only allows animals to live in harmony with their environment but food intake could also act as a zeitgeber for other rhythmic functions. Lesions in the area of the SCN result in the loss of most rhythmic functions as well as to a disrupted circadian rhythmicity of food and water intake. These findings, together with observations from daytime feeding experiments conducted in nocturnal animals, suggest that food intake may serve as a temporal signal for some peripheral organs to oscillate in phase with the SCN. This paper overviews and discusses how food intake interacts with the circadian system.     

A circadian rhythm in neural activity can be recorded from the central nervous system of the cockroach

Summary Evidence presented in this paper indicates that a robust circadian rhythm in the frequency of neural activity can be recorded from the central nervous system of intact cockroaches, Leucophaea maderae. This rhythmicity was abolished by optic lobe removal. Spontaneous neural activity was then used as an assay to demonstrate that the optic lobe is able to generate circadian oscillations in vitro. These results provide direct evidence that the cockroach optic lobe is a self-sustained circadian oscillator capable of generating daily rhythms in the absence of neural or hormonal communications with the rest of the organism.Abbreviations CNS central nervous system - DD constant dark - LD light/dark cycle - SCN suprachiasmatic nucleus - ZT Zeitgeber time     

The effects of Tat protein on locomotor activity and circadian gene expressions in the mouse hypothalamus

Transactivator (Tat), a regulatory protein of HIV-1, plays a very important role in HIV-1 infection by promoting the rapid replication of HIV. Research surrounding Tat protein function has mainly focused on inhibition of the immune system, promotion of growth of vascular endothelial cells, and nervous system damage. To date, very little research has addressed the role of Tat in circadian rhythms. Previous studies in our lab have found that the concentration of Tat protein in HIV patients’ blood was positively correlated with patients’ sleep quality and melatonin concentrations. In this study, we applied a Tat expression plasmid in mice. Result demonstrated that the locomotor activities of mice and the concentration of melatonin were significantly increased. Alternatively, the expression of Clock gene was markedly decreased. On the other hand, the expression of the Cry1 gene was significantly increased, while the expression of Bmal1 and Per1 genes exhibited no significant difference.     

Difference of social motivation in quail selected for divergent circadian activity

Endogenous rhythms are adaptive responses to predictable changes of the environment, like the day/night cycle. Some researches demonstrated that social cycles can influence the circadian rhythm, while no study investigated the effect of endogenous rhythmicity on the sociability in Vertebrates. This study investigated whether differences in the functioning of the circadian system was associated with social motivation in Japanese quail (Coturnix c. japonica).We compared quail from a line expressing a robust circadian rhythm of feeding activity (R) to quail from a line expressing circadian arrhythmicity of feeding activity (A) under constant darkness. Classic behavioral tests evaluated social motivation of these birds.When socially isolated, the motivation of R quail to re-establish contact with conspecifics appeared stronger than that of A quail. When in the presence of conspecifics, R quail faced a stressful situation (change of environment) more calmly than did A quail. Thus, variation of circadian behavioral rhythmicity is associated with variation in social motivation in Japanese quail. Rhythmic animals appeared to respond more appropriately to environmental challenges than arrhythmic animals.     

Effect of light on the development of the circadian rhythm of motor activity in the mouse

In previous experiments, we found that rats raised in constant light (LL) manifested a more robust circadian rhythm of motor activity in LL and showed longer phase shifts after a light pulse in constant darkness (DD) than those raised under constant darkness. In addition, we observed that the effects produced by constant light differed depending on the time of postnatal development in which it was given. These results suggest that both sensitivity to light and the functioning of the circadian pacemaker of the rat could be affected by the environmental conditions experienced during postembryonic development. Thus, the present experiment aimed to study whether postnatal exposure to light could also affect the circadian system of the mouse. Three groups of mice were formed: One group was raised under constant darkness during lactation (DD group), the second under constant light (LL group), and the third under light-dark cycles (LD group). After lactation, the three groups were submitted first to constant light of high intensity, then to LD cycles, and finally to constant darkness. In the DD stage, a light pulse was given. Finally, mice were submitted to constant light of low intensity. We observed that the circadian rhythm of the DD group was more disturbed under constant light than the rhythm of the LL group, and that, when light intensity increased, the period of the rhythm of the DD group lengthened more than that of the LL group. No significant differences among the groups were found in the phase shift induced by the light pulse. Therefore, it appears that DD mice are more sensitive to light than their LL counterparts. However, at present there is no evidence to affirm that the light environment experienced by the mouse during postnatal development affects the circadian pacemaker. (Chronobiology International, 18(4), 683-696, 2001)     

Seasonal change in the locomotor activity rhythm of the medaka,Oryzias latipes

A group of the medaka,Oryzias latipes (Cyprinodontidae, orange-red variety, 25 males and 25 females), was kept in an aquarium, which was placed outdoors under natural conditions from December 1984 to January 1986. Locomotor activity at three layers (upper, middle, and lower layers) was recorded with a phototransistor system in each season. In summer, the fish showed typical diurnal activity at all three layers and the activity was greater than in other seasons. However, in autumn and winter, the fish became less active and showed relatively high activity at night at the upper or middle layer and diurnal activity at the lower layer. Nocturnal activity seemed to appear when the water temperature was decreased and the photoperiod was shortened. A free-running activity rhythm was also recorded under continuous darkness (DD) in each season; however, the fish showed clear free-running activity rhythms under DD only in summer.     

Entrainment to light of circadian activity rhythms in tench (Tinca tinca)

The present article analyzes locomotor activity rhythms in Tinca tinca. To that end, three different experiments were conducted on 24 animals (20 g body weight) kept in pairs in 60-liter aquaria fitted with infrared sensors connected to a computer to continuously record fish movements. The first experiment was designed to study the endogenous circadian clock under free-running conditions [ultradian 40:40 min LD pulses and constant dark (DD)] and after shifting the LD cycle. Our results demonstrate that tench has a strictly nocturnal activity pattern, an endogenous rhythm being evident in 45.8% of the fish analyzed. The second experiment was conducted to test the influence of different photoperiods (LD 6:18, 12:12, 18:6, and 22:2) on locomotor activity, the results showing that even under an extremely long photoperiod, tench activity is restricted to dark hours. The third experiment examined the effect of light intensity on locomotor activity rhythms. When fish were exposed to decreasing light intensities (from 300:0 lux to 30:0, 3:0, and 0.3:0 lux) while maintaining a constant photoperiod (LD 12:12), the highest percentage of locomotor activity was in all cases associated with the hours of complete darkness (0 lux). In short, our results clearly show that (a) tench is a species with a strictly nocturnal behavior, and (b) daily activity rhythms gradually entrain after shifting the LD cycle and persist under free-running conditions, pointing to their circadian nature. However, light strongly influences activity rhythms, since (c) the length of the active phase is directly controlled by the photophase, and (d) strictly nocturnal behavior persists even under very dim light conditions (0.3 lux). The above findings deepen our knowledge of tench behavior, which may help to optimize the aquacultural management of this species, for example, by adjusting feeding strategies to their nocturnal behavior.     

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.     

Circadian rhythm of motor activity of the Brazilian rock cavy (Kerodon rupestris) under artificial photoperiod

Kerodon rupestris, a Brazilian caviidae rodent, lives in dry stony places. In a first experiment, seven animals were kept in LD (250:0 lux and 400:0 lux) during 40 days in each condition. In the second, four animals were kept in LD (470 lux: red dim light) for 47 days, then in LL (470 lux) for 18 days and in DD (red dim light) for 23 days. Motor activity was continuously recorded by infrared sensors. Animals showed entrained rhythms to the LD cycle being light and dark active, with higher values in phase transitions. When the light intensity was increased, four animals increased and two reduced the activity. In LL, three animals expressed an endogenous tau of 24.4, 26.5 and 24.6 h and one was arrhythmic; in DD, two expressed tau of 23.6 and 23.7 h and one was arrhythmic. Results indicate that Kerodon rupestris circadian rhythm is affected by light intensity but it is not yet possible to determine its habit.     

Eye shape and activity pattern in birds

Many aspects of an animal's ecology are associated with activity pattern, the time of day when that animal is awake and active. There are two major activity patterns: diurnal , active during the day in a light-rich, or photopic, environment, and nocturnal , active after sunset in a light-limited, or scotopic, environment. Birds are also cathemeral , or equally likely to be awake at any time of day, or crepuscular , awake and active at dawn and dusk. Each of these activity patterns is associated with different levels of ambient light. This study examines how the morphology (size and shape) of the eye varies according to these different light environments for birds in a phylogenetic context. Activity pattern has a significant influence on eye shape and size in birds. Birds that are adapted for scotopic vision have eye shapes that are optimized for visual sensitivity, with larger corneal diameters relative to axial lengths. Birds that are adapted for photopic vision have eye shapes that are optimized for visual acuity, with larger axial lengths relative to corneal diameters. Birds adapted for scotopic vision also exhibit absolutely larger corneal diameters and axial lengths than do photopic birds. The results indicate that the light level under which the bird functions has a more significant influence on eye shape than phylogeny.     

DSIP/DSIP-P and circadian motor activity of rats under continuous light

Daily intravenous injection of 30 nmol/kg DSIP (delta sleep-inducing peptide) in rats under constant illumination produced marked changes of their motor activity as compared to saline controls. Similar marked but distinctly different effects on the circadian pattern of locomotor behavior partially abolished by constant illumination were also obtained after repeated administration of 0.1 nmol/kg DSIP-P (the phosphorylated analogue of DSIP) which enhanced overall motor activity. In both instances the results additionally differed from those reported for a normal 12 hr light:dark cycle. The present results support the hypothesis that DSIP might primarily act by influencing circadian rhythmicity.     

松果体昼夜节律生物钟分子机制的研究进展

在各种非哺乳类脊椎动物中 ,松果体起着中枢昼夜节律振荡器的作用。近来 ,在鸟类松果体中相继发现了几种钟基因 ,如Per、Cry、Clock和Bmal等 ,其表达的时间变化规律与哺乳类视交叉上核 (SCN)的非常相似。钟的振荡由其自身调控反馈环路的转录和翻译组成 ,鸟类松果体和哺乳类SCN似乎具有共同的钟振荡基本分子构架 ;若干钟基因产物作为正向或负向调节子影响钟的振荡 ;昼夜性的控时机制同时也需要翻译后事件的参与。这些过程对钟振荡器的稳定性和 /或钟导引的光输入通路有着重要的调控作用     

Irradiance dependency of UV-A induced phase shifts in the locomotor activity rhythm of the field mouse Mus booduga

In the nocturnal field mouse Mus booduga, the responsiveness of the circadian system to UV-A light of 2.5 W/m² and 30 minutes duration is known to be phase dependent. The results of our experiments indicate that the phase shifts evoked by UV-A at the two phases, CT14 (circadian time 14) and CT20 increases nonlinearly with irradiance. (Chronobiology International, 17(6), 777-782, 2000)     

Daily rhythms of activity in horses housed in different stabling conditions

Total locomotor activity was studied in 10 Thoroughbreds housed under a natural 12/12 light/dark cycle. Five horses were housed in individual boxes, and five were housed in individual boxes with a paddock. In order to record locomotor activity, on each horse was placed an Actiwatch-Mini® (Cambridge Neurotechnology Ltd, UK), actigraphy-based data loggers that record a digitally integrated measure of motor activity. Locomotor activity in the different experimental conditions was evaluated by visual inspection. Average amount of activity (bout of activity/hour) during light and dark phase and cosine Peak (time of peak activity) were calculate using Actiwatch Activity Analysis 5.06. Student's t-test was used to determine significant differences. The results from this study underline the influence of stabling conditions on activity rhythms in horses; furthermore, we clearly established that in horses, the activity rhythm reaches its peak in the middle of the day.     

Exposure to T-cycles of 22 and 23 h during lactation modifies the later dissociation of motor activity and temperature circadian rhythms in rats

Early environmental conditions may affect the development and manifestation of circadian rhythms. This study sought to determine whether the maintenance of rats under different T-cycles during lactation influences the subsequent degree of dissociation of the circadian rhythms of motor activity and core body temperature. Two groups of 22 day-old Wistar rats were kept after weaning under T-cycles of 22 h (T22) or 23 h (T23) for 70 days. Subsequently, they were kept in constant darkness (DD). Half of the animals in each group were born and reared under these experimental conditions, while the other half were reared until weaning under 24 h LD cycles (T24). Rats transferred from T24 to T22 or T23 showed two circadian components in motor activity and temperature, one entrained by light and the other free-running. In T22, there was also desynchronization between temperature and motor activity. Rats submitted to T23 from birth showed higher stability of the 23 h component than rats transferred from T24 to T23 after weaning. However, in comparison to rats born under T24 and subsequently changed to T22, animals submitted to T22 from birth showed shorter values of the period of the non-light-dependent component during T22, more aftereffects when transferred to DD, and a lack of desynchronization between motor activity and temperature. The results suggest that T-cycles in the early environment may modify overt rhythms by altering the internal coupling of the circadian pacemaker.