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Articoli di riviste sul tema "Free-running rhythm"

Autore: Grafiati
Pubblicato: 4 giugno 2021
Ultima modifica: 6 febbraio 2022

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1

Kennaway, D. J., e C. F. Van Dorp. "Free-running rhythms of melatonin, cortisol, electrolytes, and sleep in humans in Antarctica". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 260, n. 6 (1 giugno 1991): R1137—R1144. http://dx.doi.org/10.1152/ajpregu.1991.260.6.r1137.

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Abstract (sommario):
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.
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2

Sailaja, B., e S. Sivaprasad. "Photoperiod-induced clock-shifting in the circadian protein and amino acid rhythms in the larval fat body of silkworm, Bombyx mori". Journal of Applied and Natural Science 3, n. 1 (1 giugno 2011): 38–50. http://dx.doi.org/10.31018/jans.v3i1.151.

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Abstract (sommario):
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.
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3

Jilge, B., H. Hornicke e H. Stahle. "Circadian rhythms of rabbits during restrictive feeding". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 253, n. 1 (1 luglio 1987): R46—R54. http://dx.doi.org/10.1152/ajpregu.1987.253.1.r46.

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Abstract (sommario):
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.
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4

Abe, Masato S., Kentarou Matsumura, Taishi Yoshii e Takahisa Miyatake. "Amplitude of circadian rhythms becomes weaken in the north, but there is no cline in the period of rhythm in a beetle". PLOS ONE 16, n. 1 (14 gennaio 2021): e0245115. http://dx.doi.org/10.1371/journal.pone.0245115.

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Abstract (sommario):
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.
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5

Dushay, M. S., R. J. Konopka, D. Orr, M. L. Greenacre, C. P. Kyriacou, M. Rosbash e J. C. Hall. "Phenotypic and genetic analysis of Clock, a new circadian rhythm mutant in Drosophila melanogaster." Genetics 125, n. 3 (1 luglio 1990): 557–78. http://dx.doi.org/10.1093/genetics/125.3.557.

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Abstract (sommario):
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.
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6

Heynick, Frank. "A geophysical note on man's free‐running circadian rhythm". Journal of Interdisiplinary Cycle Research 17, n. 2 (luglio 1986): 113–19. http://dx.doi.org/10.1080/09291018609359903.

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7

Yamada, Naoto, Kazutaka Shimoda, Ken Ohi, Saburo Takahashi e Kiyohisa Takahashi. "Free-access to a running wheel shortens the period of free-running rhythm in blinded rats". Physiology & Behavior 42, n. 1 (gennaio 1988): 87–91. http://dx.doi.org/10.1016/0031-9384(88)90265-x.

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8

Davis, Fred C., e N. Viswanathan. "Stability of circadian timing with age in Syrian hamsters". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 275, n. 4 (1 ottobre 1998): R960—R968. http://dx.doi.org/10.1152/ajpregu.1998.275.4.r960.

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Abstract (sommario):
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.
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9

Wolff, Gretchen, Marilyn J. Duncan e Karyn A. Esser. "Chronic phase advance alters circadian physiological rhythms and peripheral molecular clocks". Journal of Applied Physiology 115, n. 3 (1 agosto 2013): 373–82. http://dx.doi.org/10.1152/japplphysiol.01139.2012.

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Abstract (sommario):
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.
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10

Underwood, H., T. Siopes e K. Edmonds. "Eye and gonad: role in the dual-oscillator circadian system of female Japanese quail". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 272, n. 1 (1 gennaio 1997): R172—R182. http://dx.doi.org/10.1152/ajpregu.1997.272.1.r172.

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Abstract (sommario):
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.
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11

Reid, D. G., e E. Naylor. "Free-Running, Endogenous Semilunar Rhythmicity in a Marine Isopod Crustacean". Journal of the Marine Biological Association of the United Kingdom 65, n. 1 (febbraio 1985): 85–91. http://dx.doi.org/10.1017/s0025315400060823.

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Abstract (sommario):
In recent years several workers have postulated the occurrence in a number of coastal animals of endogenous behaviour and physiological rhythms of semilunar periodicity (see Naylor, 1982). However, only a few of these long term rhythms have been demonstrated as free-running cyclical behaviour over long periods of time in constant conditions. For example, the supra-littoral amphipod Talitrus saltator (Montagu) has been shown to express semilunar variations in daily locomotor activity over three cycles of neap/spring tides during 46 days in constant conditions in the laboratory (Williams, 1979). In contrast, in the mid-shore sand-beach isopod E. pulchra (Leach) semilunar variations in swimming behaviour (Fish & Fish, 1972; Alheit & Naylor, 1976) and of respiration (Hastings, 1981a) have so far been demonstrated only in isopods collected at various stages of the neaps/springs cycle of tides and recorded for a few days in the laboratory. It, therefore, still remains to confirm unequivocally in Eurydice, and in many other forms, which appear to show semilunar periodicity, that such rhythmicity is expressed as a free-running rhythm over long periods of time in constant conditions.
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12

Edgar, D. M., e W. C. Dement. "Regularly scheduled voluntary exercise synchronizes the mouse circadian clock". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 261, n. 4 (1 ottobre 1991): R928—R933. http://dx.doi.org/10.1152/ajpregu.1991.261.4.r928.

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Abstract (sommario):
Circadian rhythm entrainment has long been thought to depend exclusively on periodic cues in the external environment. However, evidence now suggests that appropriately timed vigorous activity may also phase shift the circadian clock. Previously it was not known whether levels of exercise/activity associated with spontaneous behavior provided sufficient feedback to phase shift or synchronize circadian rhythms. The present study investigated this issue by monitoring the sleep-wake, drinking, and wheel-running circadian rhythms of mice (Mus musculus) during unrestricted access to running wheels and when free wheel rotation was limited to either 12- or 6-h intervals with a fixed period of 24 h. Wheel rotation was controlled remotely. Mice spontaneously ran in wheels during scheduled access, and free-running sleep-wake and drinking circadian rhythms became entrained to scheduled exercise in 11 of 15 animals. However, steady-state entrainment was achieved only when exercise commenced several hours into the subjective night. The temporal placement of running during entrainment was related (r = 0.7003, P less than 0.02) to free-running period before entrainment. Mice with a free-running period less than 23.0 h did not entrain but exhibited relative coordination between free-running variables and the wheel availability schedule. Thus the circadian timekeeping system responds to temporal feedback arising from the timing of volitional exercise/activity, suggesting that the biological clock not only is responsive to periodic geophysical events in the external environment but also derives physiological feedback from the spontaneous activity behaviors of the organism.
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13

Thomas, E. M., e S. M. Armstrong. "Effect of ovariectomy and estradiol on unity of female rat circadian rhythms". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 257, n. 5 (1 novembre 1989): R1241—R1250. http://dx.doi.org/10.1152/ajpregu.1989.257.5.r1241.

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Abstract (sommario):
Sixteen rats were ovariectomized and given either a 1-cm implant of crystalline estradiol-17 beta (eight rats) or an empty implant (eight rats). A further six rats were sham ovariectomized and given empty implants, and eight rats were left unoperated. The rats were exposed to 70 days of constant dim light (LL) with a maximum illumination level of 20 lx, and circadian running and drinking rhythms were monitored. In LL, both the running and drinking activity rhythms of the ovariectomized, blank-implanted rats became markedly disrupted, whereas unoperated and sham-operated rats maintained unified rhythms. Estradiol-implanted rats developed fewer rhythm desynchronies, and the majority displayed a single band of free-running activity. Rather than being arrhythmic, the activity of the LL-exposed ovariectomized rats appeared to contain several free-running components. Thus these data are consistent with the concept of a multioscillatory basis to the circadian system and support a role for the ovary and its hormone estradiol in the maintenance of coherence between component oscillators.
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14

Cambras, Trinitat, John R. Weller, Montserrat Anglès-Pujoràs, Michael L. Lee, Andrea Christopher, Antoni Díez-Noguera, James M. Krueger e Horacio O. de la Iglesia. "Circadian desynchronization of core body temperature and sleep stages in the rat". Proceedings of the National Academy of Sciences 104, n. 18 (23 aprile 2007): 7634–39. http://dx.doi.org/10.1073/pnas.0702424104.

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Abstract (sommario):
Proper functioning of the human circadian timing system is crucial to physical and mental health. Much of what we know about this system is based on experimental protocols that induce the desynchronization of behavioral and physiological rhythms within individual subjects, but the neural (or extraneural) substrates for such desynchronization are unknown. We have developed an animal model of human internal desynchrony in which rats are exposed to artificially short (22-h) light–dark cycles. Under these conditions, locomotor activity, sleep–wake, and slow-wave sleep (SWS) exhibit two rhythms within individual animals, one entrained to the 22-h light–dark cycle and the other free-running with a period >24 h (τ>24 h). Whereas core body temperature showed two rhythms as well, further analysis indicates this variable oscillates more according to the τ>24 h rhythm than to the 22-h rhythm, and that this oscillation is due to an activity-independent circadian regulation. Paradoxical sleep (PS), on the other hand, shows only one free-running rhythm. Our results show that, similarly to humans, (i) circadian rhythms can be internally dissociated in a controlled and predictable manner in the rat and (ii) the circadian rhythms of sleep–wake and SWS can be desynchronized from the rhythms of PS and core body temperature within individual animals. This model now allows for a deeper understanding of the human timekeeping mechanism, for testing potential therapies for circadian dysrhythmias, and for studying the biology of PS and SWS states in a neurologically intact model.
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15

Robinson, Edward L., e Charles A. Fuller. "Endogenous thermoregulatory rhythms of squirrel monkeys in thermoneutrality and cold". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 276, n. 5 (1 maggio 1999): R1397—R1407. http://dx.doi.org/10.1152/ajpregu.1999.276.5.r1397.

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Whole body heat production (HP) and heat loss (HL) were examined to determine if the free-running circadian rhythm in body temperature (Tb) results from coordinated changes in HP and HL rhythms in thermoneutrality (27°C) as well as mild cold (17°C). Squirrel monkey metabolism ( n = 6) was monitored by both indirect and direct calorimetry, with telemetered measurement of Tb and activity. Feeding was also measured. Rhythms of HP, HL, and conductance were tightly coupled with the circadian Tb rhythm at both ambient temperatures (TA). At 17°C, increased HP compensated for higher HL at all phases of the Tb rhythm, resulting in only minor changes to Tb. Parallel compensatory changes of HP and HL were seen at all rhythm phases at both TA. Similar time courses of Tb, HP, and HL in their respective rhythms and the relative stability of Tb during both active and rest periods suggest action of the circadian timing system on Tb set point.
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16

Sailaja, B., e S. Sivaprasad. "Photoperiodic modulation of circadian rhythms in the silk gland protein profiles of Bombyx mori and its influence on the silk productivity and quality". Journal of Applied and Natural Science 2, n. 1 (1 giugno 2010): 48–56. http://dx.doi.org/10.31018/jans.v2i1.94.

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Abstract (sommario):
Circadian rhythms in the silk gland protein profiles of Bombyx mori were analyzed under 12 h light and 12 h dark cycle (LD), continuous light (LL) and continuous dark (DD) conditions. The phase response curves of protein rhythms indicate the prevalence of a series of silk cycles, each comprising three phases; transcription, translation and consolidation of silk proteins. In the 24h- protein rhythm, the silk cycle repeats every 3h, 42 m under LD, 2h, 36m under LL and 3h under DD. The light and dark conditions advanced the rhythm of each silk cycle by 48m and 24m respectively. As a result the silk gland completes 7 rounds of protein synthesis under LD, 9 rounds under LL and 8 rounds under DD during the 24h-free running time of the rhythm. The light-induced clock-shift in the protein rhythm caused significant gains in economic parameters of sericulture with positive signals for enhancing silk productivity and quality.
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17

Wenger, D., H. Biebach e J. R. Krebs. "Free-running circadian rhythm of a learned feeding pattern in starlings". Naturwissenschaften 78, n. 2 (febbraio 1991): 87–89. http://dx.doi.org/10.1007/bf01206266.

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18

Paolucci, Silvia, Elena Dalla Benetta, Lucia Salis, David Doležel, Louis van de Zande e Leo Beukeboom. "Latitudinal Variation in Circadian Rhythmicity in Nasonia vitripennis". Behavioral Sciences 9, n. 11 (15 novembre 2019): 115. http://dx.doi.org/10.3390/bs9110115.

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Abstract (sommario):
Many physiological processes of living organisms show circadian rhythms, governed by an endogenous clock. This clock has a genetic basis and is entrained by external cues, such as light and temperature. Other physiological processes exhibit seasonal rhythms, that are also responsive to light and temperature. We previously reported a natural latitudinal cline of photoperiodic diapause induction in the parasitic wasp Nasonia vitripennis in Europe and a correlated haplotype frequency for the circadian clock gene period (per). To evaluate if this correlation is reflected in circadian behaviour, we investigated the circadian locomotor activity of seven populations from the cline. We found that the proportion of rhythmic males was higher than females in constant darkness, and that mating decreased rhythmicity of both sexes. Only for virgin females, the free running period (τ) increased weakly with latitude. Wasps from the most southern locality had an overall shorter free running rhythm and earlier onset, peak, and offset of activity during the 24 h period, than wasps from the northernmost locality. We evaluated this variation in rhythmicity as a function of period haplotype frequencies in the populations and discussed its functional significance in the context of local adaptation.
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19

Wang, Danfeng, Guang Yang e Wenfeng Chen. "Diel and Circadian Patterns of Locomotor Activity in the Adults of Diamondback Moth (Plutella xylostella)". Insects 12, n. 8 (14 agosto 2021): 727. http://dx.doi.org/10.3390/insects12080727.

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The Diamondback Moth (Plutella xylostella) is a highly destructive lepidopteran pest of cruciferous crops. However, there still is relatively little known about the locomotor activities of diel and the circadian patterns in P. xylostella. Here, we present an analysis of the diel locomotion of P. xylostella under several laboratory settings. We established a system for measuring the individual locomotor activities of P. xylostella and found that both males and females showed a nocturnal pattern of activity under 26 or 20 °C LD conditions, with activity peaking immediately after lights off and quickly declining after lights on. In addition, we showed that it is difficult to assess the free-running circadian rhythms of P. xylostella under 26 °C DD conditions. However, we found that males showed a higher power, rhythm index (RI) and rhythmic ratio than females under 20 °C DD conditions, which indicated that males in low-temperature conditions are much more suitable to study the free-running circadian rhythms of P. xylostella. The findings of this study will help us to have a better understanding of the diel activity of P. xylostella and may provide a foundation for the development of an effective pest management strategy.
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Yamanaka, Yujiro, Sato Honma e Ken-ichi Honma. "Daily exposure to a running wheel entrains circadian rhythms in mice in parallel with development of an increase in spontaneous movement prior to running-wheel access". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 305, n. 11 (1 dicembre 2013): R1367—R1375. http://dx.doi.org/10.1152/ajpregu.00389.2013.

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Abstract (sommario):
Entrainment of circadian behavior rhythms by daily exposure to a running wheel was examined in mice under constant darkness. Spontaneous movement was individually monitored for more than 6 mo by a thermal sensor. After establishment of steady-state free running, mice were placed in a different cage equipped with a running-wheel for 3 h once per day at 6 AM. The daily exchange was continued for 80 days. The number of wheel revolutions during exposure to the running wheel was also measured simultaneously with spontaneous movement. In 13 out of 17 mice, circadian behavior rhythm was entrained by daily wheel exposure, showing a period indistinguishable from 24 h. The entrainment occurred in parallel with an increase in spontaneous movement immediately prior to the daily wheel exposure. A similar preexposure increase was observed in only one of four nonentrained mice. The preexposure increase appeared in 19.5 days on average after the start of daily wheel exposure and persisted for 36 days on average after the termination of the exposure schedule. The preexposure increase was detected only when daily wheel exposure came into the activity phase of the circadian behavior rhythm, which was accompanied by an increase in the number of wheel revolutions. These findings indicate that a novel oscillation with a circadian period is induced in mice by daily exposure to a running wheel at a fixed time of day and suggest that the oscillation is involved in the nonphotic entrainment of circadian rhythms in spontaneous movement.
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Kuroda, H. "Daily Wheel Running Activity Modifies the Period of Free-Running Rhythm in Rats Via Intergeniculate Leaflet". Physiology & Behavior 61, n. 5 (maggio 1997): 633–37. http://dx.doi.org/10.1016/s0031-9384(96)00457-x.

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22

Wollnik, F., e F. W. Turek. "SCN lesions abolish ultradian and circadian components of activity rhythms in LEW/Ztm rats". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 256, n. 5 (1 maggio 1989): R1027—R1039. http://dx.doi.org/10.1152/ajpregu.1989.256.5.r1027.

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Abstract (sommario):
A trimodal locomotor activity pattern has been observed in LEW/Ztm rats. Complete and partial lesions of the suprachiasmatic nucleus (SCN) were used to determine whether the same neural substrate may underlie the circadian rhythms and the ultradian modulation of wheel-running activity in these rats. Whereas sham lesions had little or no effect on the wheel-running activity pattern, complete SCN lesions resulted in a complete loss of circadian and ultradian activity components under free-running or 12:12 h light-dark cycle (12:12 LD) conditions. Ultradian and circadian activity components were still present after partial SCN lesions. Periodogram analysis for any given animal revealed that the ultradian periods were always submultiples of the entrained or free-running circadian period. Furthermore there was a high correlation between the amplitudes of circadian and ultradian spectral estimates, but with a different slope in males and females. These results indicate that in LEW/Ztm rats the SCN contributes to the control of both the circadian wheel-running rhythm and the trimodal ultradian modulation of that behavior.
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23

Hill, Elizabeth Anne. "Free-running circadian rhythm disorder in the sighted – case report & discussion". Res Medica 21, n. 1 (30 settembre 2013): 50. http://dx.doi.org/10.2218/resmedica.v21i1.174.

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Tsujimaru, Shusaku, Hideaki Egami, Goro Honma, Yoshishige Ida, Hirotaka Mukasa e Yoichi Nakazawa. "Effects of Vitamin B12on the Period of Free-Running Rhythm in Rats". Psychiatry and Clinical Neurosciences 46, n. 1 (marzo 1992): 225–26. http://dx.doi.org/10.1111/j.1440-1819.1992.tb00843.x.

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Kyorku, Charles, e John Brady. "A free-running bimodal circadian rhythm in the tsetse fly Glossina longipennis". Journal of Insect Physiology 40, n. 1 (gennaio 1994): 63–67. http://dx.doi.org/10.1016/0022-1910(94)90112-0.

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26

Northcott, S. J., R. N. Gibson e E. Morgan. "The persistence and modulation of endogenous circatidal rhythmicity in Lipophrys pholis (Teleostei)". Journal of the Marine Biological Association of the United Kingdom 70, n. 4 (novembre 1990): 815–27. http://dx.doi.org/10.1017/s0025315400059087.

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Abstract (sommario):
In constant conditions, freshly-collected Lipophrys pholis show an endogenous circatidal activity rhythm, the initial activity peaks of which are phased to the expected time of high tide. The rhythm usually damps out over a few days but it may re-appear spontaneously or as a result of disturbance caused by handling and transfer to the experimental apparatus. The free-running period is more variable in fish kept in non-tidal conditions for prolonged periods than in those recorded shortly after capture. The non-circatidal periodicity shown by some fish may be the result of stable coupling in antiphase of desynchronised oscillators. There is no semilunar variation of the circatidal rhythm and no influence of the slight diurnal inequality in tidal period upon the rhythm's periodicity, at least at the site studied. The activity rhythm of Lipophrys varies seasonally.
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27

Abe, H., e B. Rusak. "Anticipatory activity and entrainment of circadian rhythms in Syrian hamsters exposed to restricted palatable diets". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 263, n. 1 (1 luglio 1992): R116—R124. http://dx.doi.org/10.1152/ajpregu.1992.263.1.r116.

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Abstract (sommario):
Activity rhythms were recorded from hamsters in three conditions: during timed feedings of an attractive diet with free access to regular food, during restriction to 70% of normal food consumption, and during moderate food deprivation with limited temporal access to an attractive diet. An attractive diet given to intact animals did not induce anticipatory activity or entrainment, but damage to the suprachiasmatic nuclei (SCN) led to the development of anticipatory activity. Food restriction to 70% of normal intake led to anticipatory components in some intact animals, without entraining the dominant circadian pacemaker. The combination of a palatable diet and food restriction led to anticipatory activity before the daily feeding times and entrainment of a previously free-running circadian rhythm in some animals. Ablation of the SCN did not eliminate anticipatory activity in experimental animals, but did eliminate the free-running component of the rhythms. These results indicate that hamsters have a mechanism separate from the SCN that can anticipate daily feeding times, as rats do, and that they may show entrainment of the SCN-based pacemaker to such feeding schedules.
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28

Matsumura, Kentarou, Masato S. Abe, Manmohan D. Sharma, David J. Hosken, Taishi Yoshii e Takahisa Miyatake. "Genetic variation and phenotypic plasticity in circadian rhythms in an armed beetle, Gnatocerus cornutus (Tenebrionidae)". Biological Journal of the Linnean Society 130, n. 1 (7 marzo 2020): 34–40. http://dx.doi.org/10.1093/biolinnean/blaa016.

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Abstract (sommario):
Abstract Circadian rhythms, their free-running periods and the power of the rhythms are often used as indicators of biological clocks, and there is evidence that the free-running periods of circadian rhythms are not affected by environmental factors, such as temperature. However, there are few studies of environmental effects on the power of the rhythms, and it is not clear whether temperature compensation is universal. Additionally, genetic variation and phenotypic plasticity in biological clocks are important for understanding the evolution of biological rhythms, but genetic and plastic effects are rarely investigated. Here, we used 18 isofemale lines (genotypes) of Gnatocerus cornutus to assess rhythms of locomotor activity, while also testing for temperature effects. We found that total activity and the power of the circadian rhythm were affected by interactions between sex and genotype or between sex, genotype and temperature. The males tended to be more active and showed greater increases in activity, but this effect varied across both genotypes and temperatures. The period of activity varied only by genotype and was thus independent of temperature. The complicated genotype–sex–environment interactions we recorded stress the importance of investigating circadian activity in more integrated ways.
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29

Tran, Damien, Mickael Perrigault, Pierre Ciret e Laura Payton. "Bivalve mollusc circadian clock genes can run at tidal frequency". Proceedings of the Royal Society B: Biological Sciences 287, n. 1918 (8 gennaio 2020): 20192440. http://dx.doi.org/10.1098/rspb.2019.2440.

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Abstract (sommario):
Marine coastal habitats are complex cyclic environments as a result of sun and moon interactions. In contrast with the well-known circadian orchestration of the terrestrial animal rhythmicity (approx. 24 h), the mechanism responsible for the circatidal rhythm (approx. 12.4 h) remains largely elusive in marine organisms. We revealed in subtidal field conditions that the oyster Crassostrea gigas exhibits tidal rhythmicity of circadian clock genes and clock-associated genes. A free-running (FR) experiment showed an endogenous circatidal rhythm. In parallel, we showed in the field that oysters' valve behaviour exhibited a strong tidal rhythm combined with a daily rhythm. In the FR experiment, all behavioural rhythms were circatidal, and half of them were also circadian. Our results fuel the debate on endogenous circatidal mechanisms. In contrast with the current hypothesis on the existence of an independent tidal clock, we suggest that a single ‘circadian/circatidal’ clock in bivalves is sufficient to entrain behavioural patterns at tidal and daily frequencies.
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30

Abelló, P., D. G. Reid e E. Naylor. "Comparative locomotor activity patterns in the portunid crabs Liocarcinus holsatus and L. depurator". Journal of the Marine Biological Association of the United Kingdom 71, n. 1 (febbraio 1991): 1–10. http://dx.doi.org/10.1017/s0025315400037346.

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Abstract (sommario):
The free-running locomotor activity rhythms of freshly-captured swimming crabs Liocarcinus holsatus and L. depurator have been studied in constant conditions in the laboratory. L. holsatus captured in the intertidal zone of sandy beaches showed strong circatidal activity rhythms with maximum activity at high tide. L. holsatus captured in the sublittoral zone had a clear tendency to show circadian activity rhythms with highest activity during day-time hours. L. depurator occurred only sublittorally and showed circadian activity patterns with highest activity during the night. Exposure to hydrostatic pressure cycles of tidal amplitude and periodicity, entrained strong circatidal activity rhythms in previously arhythmic L. holsatus. This activity pattern also showed a marked circadian component. Exposure to the same regime entrained a circadian rhythm, but not a circatidal rhythm in L. depurator. In the sublittoral zone L. depurator is active mainly during the night, whereas L. holsatus, is active mainly during the day. This may constitute a behavioural mechanism for minimizing competitive interactions between these two sympatric crabs.
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31

Poulis, J. A., F. Roelfsema e D. van der Heide. "Circadian urinary excretion rhythms in adrenalectomized rats". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 251, n. 3 (1 settembre 1986): R441—R449. http://dx.doi.org/10.1152/ajpregu.1986.251.3.r441.

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Abstract (sommario):
The impact of the adrenal system on urinary rhythms was investigated in adrenalectomized (ADX) rats under various experimental conditions. During a 12:12 light-dark cycle the acrophases were shifted in ADX rats with respect to control rats. Under constant light conditions ADX rats displayed free-running rhythms, similar to those of control rats. The periods were stable in blind rats but not in rats maintained on a constant light cycle. The abrupt change in period, which occurred after approximately 8 days, suggests a stage of internal desynchronization. A 6-h delay in the administration of corticosterone to ADX rats caused a delay shift of the acrophases. A single intraperitoneal injection of corticosterone in blind free-running ADX rats caused delay or advance shifts so that we could construct phase-response curves for the various excretory rhythms. These observations indicate that the adrenals are not essential for the establishment of the urinary rhythms; however, corticosterone influences the phase setting of these rhythms. The site of action is probably the X pacemaker (controlling the body temperature rhythm), although we cannot totally exclude an additional effect on secondary (renal) oscillators.
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32

Lax, Pedro, Salvador Zamora e Juan A. Madrid. "Coupling effect of locomotor activity on the rat’s circadian system". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 275, n. 2 (1 agosto 1998): R580—R587. http://dx.doi.org/10.1152/ajpregu.1998.275.2.r580.

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Abstract (sommario):
Exercise is recognized to affect circadian rhythmicity in a variety of ways. It masks the expression of other behavioral and physiological rhythms, entrains the master pacemaker, and influences the free-running period of other rhythms. In this paper we study the influence of exercise on the organization of the timing system by analyzing the effect of voluntary locomotor activity on the circadian feeding behavior of rats subjected to different lighting conditions. The availability of wheel running prevented loss of feeding circadian rhythmicity under constant bright light (LL) but did not elicit any circadian pattern in rats showing a previous arrhythmic pattern. Under dim red light (DR), the rhythm was more pronounced in exercising than in sedentary rats, while wheel-running availability accelerated the emergence of circadian rhythmicity in arrhythmic animals that were moved from LL to DR. These results can be explained by the existence of a positive feedback loop between physical exercise and its pacemaker and also suggest that exercise changes the functioning of the circadian system to facilitate the emergence of circadian rhythms in previously arrhythmic animals.
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33

Van Reeth, O., e F. W. Turek. "Daily injections of triazolam induce long-term changes in hamster circadian period". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 259, n. 3 (1 settembre 1990): R514—R520. http://dx.doi.org/10.1152/ajpregu.1990.259.3.r514.

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Abstract (sommario):
Previous experiments in hamsters indicate that daily injections of the short-acting benzodiazepine, triazolam, can entrain the free-running circadian activity rhythm to the period of the injections and that, after discontinuation of triazolam injections, the period of the free-running activity rhythm remains close to that of the previous injection schedule for 20-50 cycles. In this paper, we extend these findings and demonstrate that 1) long-term treatment with triazolam can induce aftereffects on the period of the circadian clock underlying the activity rhythm that can last for up to 100 days, 2) triazolam-induced changes in period can lead to a loss of effect of daily injections of triazolam which can be restored if the time of injection is altered, and 3) chronic treatment with triazolam also alters the period of the circadian clock in animals entrained to a light-dark cycle, and such changes in period alter the phase relationship between the circadian clock and the entraining light-dark cycle.
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34

Bulthuis, Nicholas, Katrina R. Spontak, Benjamin Kleeman e Daniel J. Cavanaugh. "Neuronal Activity in Non-LNv Clock Cells Is Required to Produce Free-Running Rest:Activity Rhythms in Drosophila". Journal of Biological Rhythms 34, n. 3 (17 aprile 2019): 249–71. http://dx.doi.org/10.1177/0748730419841468.

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Abstract (sommario):
Circadian rhythms in behavior and physiology are produced by central brain clock neurons that can be divided into subpopulations based on molecular and functional characteristics. It has become clear that coherent behavioral rhythms result from the coordinated action of these clock neuron populations, but many questions remain regarding the organizational logic of the clock network. Here we used targeted genetic tools in Drosophila to eliminate either molecular clock function or neuronal activity in discrete clock neuron subsets. We find that neuronal firing is necessary across multiple clock cell populations to produce free-running rhythms of rest and activity. In contrast, such rhythms are much more subtly affected by molecular clock suppression in the same cells. These findings demonstrate that network connectivity can compensate for a lack of molecular oscillations within subsets of clock cells. We further show that small ventrolateral (sLNv) clock neurons, which have been characterized as master pacemakers under free-running conditions, cannot drive rhythms independent of communication between other cells of the clock network. In particular, we pinpoint an essential contribution of the dorsolateral (LNd) clock neurons, and show that manipulations that affect LNd function reduce circadian rhythm strength without affecting molecular cycling in sLNv cells. These results suggest a hierarchical organization in which circadian information is first consolidated among one or more clock cell populations before accessing output pathways that control locomotor activity.
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35

Seggio, Joseph A., Bernard Possidente e S. Tariq Ahmad. "Larval Ethanol Exposure Alters Adult Circadian Free-Running Locomotor Activity Rhythm inDrosophila melanogaster". Chronobiology International 29, n. 1 (4 gennaio 2012): 75–81. http://dx.doi.org/10.3109/07420528.2011.635236.

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36

Greene, Andrew V., Nancy Keller, Hubertus Haas e Deborah Bell-Pedersen. "A Circadian Oscillator in Aspergillus spp. Regulates Daily Development and Gene Expression". Eukaryotic Cell 2, n. 2 (aprile 2003): 231–37. http://dx.doi.org/10.1128/ec.2.2.231-237.2003.

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Abstract (sommario):
ABSTRACT We have established the presence of a circadian clock in Aspergillus flavus and Aspergillus nidulans by morphological and molecular assays, respectively. In A. flavus, the clock regulates an easily assayable rhythm in the development of sclerotia, which are large survival structures produced by many fungi. This developmental rhythm exhibits all of the principal clock properties. The rhythm is maintained in constant environmental conditions with a period of 33 h at 30°C, it can be entrained by environmental signals, and it is temperature compensated. This endogenous 33-h period is one of the longest natural circadian rhythms reported for any organism, and this likely contributes to some unique responses of the clock to environmental signals. In A. nidulans, no obvious rhythms in development are apparent. However, a free running and entrainable rhythm in the accumulation of gpdA mRNA (encoding glyceraldehyde-3-phosphate dehydrogenase) is observed, suggesting the presence of a circadian clock in this species. We are unable to identify an Aspergillus ortholog of frequency, a gene required for normal circadian rhythmicity in Neurospora crassa. Together, our data indicate the existence of an Aspergillus circadian clock, which has properties that differ from that of the well-described clock of N. crassa.
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37

Masana, Monica I., Isabel C. Sumaya, Michael Becker-Andre e Margarita L. Dubocovich. "Behavioral characterization and modulation of circadian rhythms by light and melatonin in C3H/HeN mice homozygous for the RORβ knockout". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 292, n. 6 (giugno 2007): R2357—R2367. http://dx.doi.org/10.1152/ajpregu.00687.2006.

Testo completo
Abstract (sommario):
This study reports for the first time the effects of retinoid-related orphan receptors [RORβ; receptor gene deletion RORβ(C3H)−/−] in C3H/HeN mice on behavioral and circadian phenotypes. Pineal melatonin levels showed a robust diurnal rhythm with high levels at night in wild-type (+/+), heterozygous (+/−), and knockout (−/−) mice. The RORβ(C3H)−/− mice displayed motor (“duck gait,” hind paw clasping reflex) and olfactory deficits, and reduced anxiety and learned helplessness-related behaviors. Circadian rhythms of wheel-running activity in all genotypes showed entrainment to the light-dark (LD) cycle, and free running in constant dark, with RORβ(C3H)−/− mice showing a significant increase in circadian period ( tau). Melatonin administration (90 μg/mouse sc for 3 days) at circadian time (CT) 10 induced phase advances, while exposure to a light pulse (300 lux) at CT 14 induced phase delays of circadian activity rhythms of the same magnitude in all genotypes. In RORβ(C3H)−/− mice a light pulse at CT 22 elicited a larger phase advance in activity rhythms and a slower rate of reentrainment after a 6-h advance in the LD cycle compared with (+/+) mice. Yet, the rate of reentrainment was significantly advanced by melatonin administration at the new dark onset in both (+/+) and (−/−) mice. We conclude that the RORβ nuclear receptor is not involved in either the rhythmic production of pineal melatonin or in mediating phase shifts of circadian rhythms by melatonin, but it may regulate clock responses to photic stimuli at certain time domains.
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38

Laakso, M. L., T. Porkka-Heiskanen, L. Leinonen, S. L. Joutsiniemi e P. T. Mannisto. "Hormonal and locomotor activity rhythms in rats under 90-min dark-pulse conditions". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 264, n. 6 (1 giugno 1993): R1058—R1064. http://dx.doi.org/10.1152/ajpregu.1993.264.6.r1058.

Testo completo
Abstract (sommario):
The ability of a short dark pulse to entrain the circadian rhythms in rats was investigated. Pineal melatonin contents and serum levels of corticosterone and thyrotropin, a thyroid-stimulating hormone (TSH), were measured and locomotor activity was recorded under 12:12-h light-dark cycles (LD; darkness from 1800 to 0600 h) and under a 22.5:1.5 h LD lighting schedule (darkness from 1800 to 1930 h). The 90-min dark pulse was enough to trigger the rise of melatonin synthesis, but a free-running component was detected in the locomotor activity. Corticosterone levels showed diurnal variations under both conditions. The decrease of corticosterone and the increase of melatonin were phase locked, but the corticosterone pattern was distorted under the dark-pulse conditions. The 24-h rhythm of TSH was detectable in the control but not in the dark-pulse schedule. The results suggest that the circadian rhythm of pineal melatonin and the decrease of serum corticosterone levels were entrainable by the dark pulses, whereas the increase of corticosterone, the variations of TSH, and the rhythm of locomotor activity were not.
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39

HONMA, Ken-ichi, Sato HONMA e Tsutomu HIROSHIGE. "Response curve, free-running period, and activity time in circadian locomotor rhythm of rats." Japanese Journal of Physiology 35, n. 4 (1985): 643–58. http://dx.doi.org/10.2170/jjphysiol.35.643.

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40

Takahashi, Kiyohisa, Mizuo Takashima, Ken Ohi, Naoto Yamada e Kazutaka Shimoda. "Environmental factors influencing the free-running period of locomotor activity rhythm in blinded rats". Neuroscience Research Supplements 5 (gennaio 1987): S134. http://dx.doi.org/10.1016/0921-8696(87)90281-7.

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41

Kitamura, Shingo, Akiko Hida, Minori Enomoto, Makiko Watanabe, Yasuko Katayose, Kentaro Nozaki, Sayaka Aritake et al. "Intrinsic Circadian Period of Sighted Patients with Circadian Rhythm Sleep Disorder, Free-Running Type". Biological Psychiatry 73, n. 1 (gennaio 2013): 63–69. http://dx.doi.org/10.1016/j.biopsych.2012.06.027.

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42

McMeechan, Fiona K., Andrea Manica e William A. Foster. "Rhythms of activity and foraging in the intertidal insect Anurida maritima: coping with the tide". Journal of the Marine Biological Association of the United Kingdom 80, n. 1 (febbraio 2000): 189–90. http://dx.doi.org/10.1017/s0025315499001770.

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Abstract (sommario):
The intertidal insect Anurida maritima (Apterygota: Collembola) has a circatidal rhythm of locomotory activity on the soil surface which was observed during both the day and the night. The main function of this activity was foraging for food. When a superabundant food supply was provided on the upper shore, this completely repressed the usual migration to the lower shore. There was a clear rhythm in feeding activity which was highest shortly after the sea uncovered the insects' shelters and declined rapidly during the intertidal period. The circatidal rhythm of locomotory activity persisted in the laboratory in constant light for seven days (15 cycles). A free-running rhythm underlying the degree of aggregation was also detected.
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43

Steiger, Silke S., Mihai Valcu, Kamiel Spoelstra, Barbara Helm, Martin Wikelski e Bart Kempenaers. "When the sun never sets: diverse activity rhythms under continuous daylight in free-living arctic-breeding birds". Proceedings of the Royal Society B: Biological Sciences 280, n. 1764 (7 agosto 2013): 20131016. http://dx.doi.org/10.1098/rspb.2013.1016.

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Abstract (sommario):
Circadian clocks are centrally involved in the regulation of daily behavioural and physiological processes. These clocks are synchronized to the 24 h day by external cues ( Zeitgeber ), the most important of which is the light–dark cycle. In polar environments, however, the strength of the Zeitgeber is greatly reduced around the summer and winter solstices (continuous daylight or continuous darkness). How animals time their behaviour under such conditions has rarely been studied in the wild. Using a radio-telemetry-based system, we investigated daily activity rhythms under continuous daylight in Barrow, Alaska, throughout the breeding season in four bird species that differ in mating system and parental behaviour. We found substantial diversity in daily activity rhythms depending on species, sex and breeding stage. Individuals exhibited either robust, entrained 24 h activity cycles, were continuously active (arrhythmic) or showed ‘free-running’ activity cycles. In semipalmated sandpipers, a shorebird with biparental incubation, we show that the free-running rhythm is synchronized between pair mates. The diversity of diel time-keeping under continuous daylight emphasizes the plasticity of the circadian system, and the importance of the social and life-history context. Our results support the idea that circadian behaviour can be adaptively modified to enable species-specific time-keeping under polar conditions.
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44

Ono, Daisuke, Sato Honma, Yoshihiro Nakajima, Shigeru Kuroda, Ryosuke Enoki e Ken-ichi Honma. "Dissociation of Per1 and Bmal1 circadian rhythms in the suprachiasmatic nucleus in parallel with behavioral outputs". Proceedings of the National Academy of Sciences 114, n. 18 (17 aprile 2017): E3699—E3708. http://dx.doi.org/10.1073/pnas.1613374114.

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Abstract (sommario):
The temporal order of physiology and behavior in mammals is primarily regulated by the circadian pacemaker located in the hypothalamic suprachiasmatic nucleus (SCN). Taking advantage of bioluminescence reporters, we monitored the circadian rhythms of the expression of clock genes Per1 and Bmal1 in the SCN of freely moving mice and found that the rate of phase shifts induced by a single light pulse was different in the two rhythms. The Per1-luc rhythm was phase-delayed instantaneously by the light presented at the subjective evening in parallel with the activity onset of behavioral rhythm, whereas the Bmal1-ELuc rhythm was phase-delayed gradually, similar to the activity offset. The dissociation was confirmed in cultured SCN slices of mice carrying both Per1-luc and Bmal1-ELuc reporters. The two rhythms in a single SCN slice showed significantly different periods in a long-term (3 wk) culture and were internally desynchronized. Regional specificity in the SCN was not detected for the period of Per1-luc and Bmal1-ELuc rhythms. Furthermore, neither is synchronized with circadian intracellular Ca2+ rhythms monitored by a calcium indicator, GCaMP6s, or with firing rhythms monitored on a multielectrode array dish, although the coupling between the circadian firing and Ca2+ rhythms persisted during culture. These findings indicate that the expressions of two key clock genes, Per1 and Bmal1, in the SCN are regulated in such a way that they may adopt different phases and free-running periods relative to each other and are respectively associated with the expression of activity onset and offset.
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45

Colwell, Christopher S., Stephan Michel, Jason Itri, Williams Rodriguez, J. Tam, Vincent Lelievre, Zhou Hu, X. Liu e James A. Waschek. "Disrupted circadian rhythms in VIP- and PHI-deficient mice". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 285, n. 5 (novembre 2003): R939—R949. http://dx.doi.org/10.1152/ajpregu.00200.2003.

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Abstract (sommario):
The related neuropeptides vasoactive intestinal peptide (VIP) and peptide histidine isoleucine (PHI) are expressed at high levels in the neurons of the suprachiasmatic nucleus (SCN), but their function in the regulation of circadian rhythms is unknown. To study the role of these peptides on the circadian system in vivo, a new mouse model was developed in which both VIP and PHI genes were disrupted by homologous recombination. In a light-dark cycle, these mice exhibited diurnal rhythms in activity which were largely indistinguishable from wild-type controls. In constant darkness, the VIP/PHI-deficient mice exhibited pronounced abnormalities in their circadian system. The activity patterns started ∼8 h earlier than predicted by the previous light cycle. In addition, lack of VIP/PHI led to a shortened free-running period and a loss of the coherence and precision of the circadian locomotor activity rhythm. In about one-quarter of VIP/PHI mice examined, the wheel-running rhythm became arrhythmic after several weeks in constant darkness. Another striking example of these deficits is seen in the split-activity patterns expressed by the mutant mice when they were exposed to a skeleton photoperiod. In addition, the VIP/PHI-deficient mice exhibited deficits in the response of their circadian system to light. Electrophysiological analysis indicates that VIP enhances inhibitory synaptic transmission within the SCN of wild-type and VIP/PHI-deficient mice. Together, the observations suggest that VIP/PHI peptides are critically involved in both the generation of circadian oscillations as well as the normal synchronization of these rhythms to light.
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46

Ruby, N. F., A. Saran, T. Kang, P. Franken e H. C. Heller. "Siberian hamsters free run or become arrhythmic after a phase delay of the photocycle". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 271, n. 4 (1 ottobre 1996): R881—R890. http://dx.doi.org/10.1152/ajpregu.1996.271.4.r881.

Testo completo
Abstract (sommario):
Body temperature (Tb) and locomotor activity were recorded telemetrically from male Siberian hamsters (Phodopus sungorus sungorus) that were 3 or 12 mo of age and maintained in a light-dark (LD) cycle of 16 h light/day for 2-4 mo. After 3 wk of Tb recording, the LD cycle was phase delayed by extending the light phase by 5 h for 1 day; animals remained on a 16:8-h LD cycle for the remainder of the experiment. Tb and activity rhythms of all animals were stably entrained to the LD cycle before the phase shift. After the phase shift, > or = 80% of the animals in each age group failed to reentrain and expressed free-running Tb rhythms with stable periods that ranged from 24.33 to 26.33 h; one hamster in each age group reentrained within several days. Tb became arrhythmic in 10% of all animals immediately after, and in 28% of free running animals several weeks after, the phase shift. Changes in tau and phase of activity rhythms closely paralleled Tb rhythms in individual hamsters. Daily mean Tb was unchanged, but Tb rhythm amplitude decreased by 25-50% in individual animals after the phase shift. We believe this to be the first report of neurologically intact animals failing to reentrain to a phase shift of the LD cycle. These phenomena are not readily explained by current knowledge of circadian systems and suggest that the entrainment process in Siberian hamsters differs markedly from that in other rodent species.
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47

Gilberstadt, M. L., L. L. Bellinger, S. Lindblad e W. C. Duane. "Liver denervation does not alter the circadian rhythm of bile acid synthesis in rats". American Journal of Physiology-Gastrointestinal and Liver Physiology 261, n. 5 (1 novembre 1991): G799—G802. http://dx.doi.org/10.1152/ajpgi.1991.261.5.g799.

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Abstract (sommario):
In both rats and humans there is a distinct circadian rhythm of bile acid synthesis that is independent of feedback regulation. To determine whether the circadian rhythm is directly mediated via hepatic nerves, bile acid synthesis was studied in selectively liver-denervated male Sprague-Dawley rats in a bile fistula model. Complete denervation was confirmed by histofluorescent staining for neural elements in frozen sections of livers. There was no significant difference in mean bile acid synthesis, amplitude of the circadian rhythm, or time of peak synthesis between the denervated rats and nondenervated controls. In one denervated rat studied four times at weekly intervals, there was no shift in acrophase, indicating that the rhythm had not become free running. We conclude that signals arriving via hepatic nerves neither directly cause nor entrain the circadian rhythm of bile acid synthesis in rats.
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48

Eskandari, Rosa, Lalanthi Ratnayake e Patricia L. Lakin-Thomas. "Shared Components of the FRQ-Less Oscillator and TOR Pathway Maintain Rhythmicity in Neurospora". Journal of Biological Rhythms 36, n. 4 (7 aprile 2021): 329–45. http://dx.doi.org/10.1177/0748730421999948.

Testo completo
Abstract (sommario):
Molecular models for the endogenous oscillators that drive circadian rhythms in eukaryotes center on rhythmic transcription/translation of a small number of “clock genes.” Although substantial evidence supports the concept that negative and positive transcription/translation feedback loops (TTFLs) are responsible for regulating the expression of these clock genes, certain rhythms in the filamentous fungus Neurospora crassa continue even when clock genes ( frq, wc-1, and wc-2) are not rhythmically expressed. Identification of the rhythmic processes operating outside of the TTFL has been a major unresolved area in circadian biology. Our lab previously identified a mutation ( vta) that abolishes FRQ-less rhythmicity of the conidiation rhythm and also affects rhythmicity when FRQ is functional. Further studies identified the vta gene product as a component of the TOR (Target of Rapamycin) nutrient-sensing pathway that is conserved in eukaryotes. We now report the discovery of TOR pathway components including GTR2 (homologous to the yeast protein Gtr2, and RAG C/D in mammals) as binding partners of VTA through co-immunoprecipitation (IP) and mass spectrometry analysis using a VTA-FLAG strain. Reciprocal IP with GTR2-FLAG found VTA as a binding partner. A Δ gtr2 strain was deficient in growth responses to amino acids. Free-running conidiation rhythms in a FRQ-less strain were abolished in Δ gtr2. Entrainment of a FRQ-less strain to cycles of heat pulses demonstrated that Δ gtr2 is defective in entrainment. In all of these assays, Δ gtr2 is similar to Δ vta. In addition, expression of GTR2 protein was found to be rhythmic across two circadian cycles, and functional VTA was required for GTR2 rhythmicity. FRQ protein exhibited the expected rhythm in the presence of GTR2 but the rhythmic level of FRQ dampened in the absence of GTR2. These results establish association of VTA with GTR2, and their role in maintaining functional circadian rhythms through the TOR pathway.
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49

Strogatz, S. H., R. E. Kronauer e C. A. Czeisler. "Circadian pacemaker interferes with sleep onset at specific times each day: role in insomnia". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 253, n. 1 (1 luglio 1987): R172—R178. http://dx.doi.org/10.1152/ajpregu.1987.253.1.r172.

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Abstract (sommario):
The human circadian pacemaker modulates our desire and ability to fall asleep at different times of day. To study this circadian component of sleep tendency, we have analyzed the sleep-wake patterns recorded from 15 free-running subjects in whom the sleep-wake cycle spontaneously desynchronized from the circadian rhythm of body temperature. The analysis indicates that the distribution of sleep onsets during free run is bimodal, with one peak at the temperature trough and, contrary to previous reports, a second peak 9-10 h later. Furthermore, there are two consistent zones in the circadian temperature cycle during which normal subjects rarely fall asleep. We hypothesize that this bimodal rhythm of sleep tendency, revealed under free-running conditions, maintains the same fixed phase relation to the circadian temperature cycle during 24-h entrainment. This would imply that normally entrained individuals should experience a peak of sleep tendency in the midafternoon and a zone of minimal sleep tendency approximately 1-3 h before habitual bedtime. Our temporal isolation data thereby account quantitatively for the timing of the afternoon siesta and suggest that malfunctions of the phasing of the circadian pacemaker may underlie the insomnia associated with sleep-scheduling disorders.
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50

Maywood, E. S., M. H. Hastings, M. Max, E. Ampleford, M. Menaker e A. S. I. Loudon. "Circadian and daily rhythms of melatonin in the blood and pineal gland of free-running and entrained Syrian hamsters". Journal of Endocrinology 136, n. 1 (gennaio 1993): 65–73. http://dx.doi.org/10.1677/joe.0.1360065.

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Abstract (sommario):
ABSTRACT The aim of this study was to develop a radioimmunoassay for the measurement of endogenous circulating melatonin concentrations in the Syrian hamster, and then to determine the effect of various photic manipulations upon this endocrine signal. In experiment 1, pineal-intact or pinealectomized adult male Syrian hamsters, housed under a long photoperiod (LD; 16 h light:8 h darkness) for 2 weeks, were then either maintained on LD or transferred to a short photoperiod (SD; 8 h light:16 h darkness) for a further 8 weeks. The profile of serum melatonin concentrations was determined from blood samples taken by cardiac puncture at intervals over a 24-h period. Radioimmunoassay revealed that daytime concentrations were at or below the limit of sensitivity of the assay (≥ 50 pmol/l). Under both photoperiods, the concentration of melatonin in the serum of pineal-intact animals rose 4–5 h after the onset of darkness, and the peak amplitude of the melatonin rhythm was not significantly different between the SD- or LD-housed animals (200–250 pmol/l). Premature exposure of animals to light during the dark phase of LD caused a precipitous decline in circulating concentrations to daytime values within 15 min and they remained there for several hours. In animals which experienced an uninterrupted night on either LD or SD, the most striking difference in the rhythm of endogenous melatonin secretion was the duration. Animals housed under LD had high levels until the start of the light period, a peak duration of 3·7 h. In contrast, animals housed under SD exhibited a peak duration of 10 h, levels falling 1·5 h before the start of the light period. The nocturnal increase in serum melatonin concentration was abolished in pinealectomized animals. Serum levels in these animals were not significantly different from those observed in pineal-intact animals during the light phase, being at, or very close to, the limit of sensitivity of the assay. In experiment 2, animals were housed under LD prior to transfer to continuous darkness for 10 days, during which time their locomotor activity rhythms were recorded. Animals were then chronically cannulated and serial blood samples were removed from the jugular vein at hourly intervals, starting 48 h after surgery. A pronounced circadian rhythm in plasma melatonin concentrations was observed, with levels rising significantly 3 h after the onset of activity and falling 10 h later. During subjective day, levels were at or below the limit of sensitivity of the assay. At the end of the study, pineal melatonin was also measured at intervals across the circadian cycle. This revealed a very close correlation between the plasma and pineal concentrations of melatonin, the duration and phase of both nocturnal peaks being equivalent. These results confirm that the duration of the nocturnal secretion of melatonin varies in proportion to the length of the dark phase, that this rhythm is endogenously driven, and that peak physiological levels of melatonin in this species are of the order of 200 pmol/l. Journal of Endocrinology (1993) 136, 65–73
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