Disorganization of the rat activity rhythm by chronic treatment with methamphetamine

Remarkable changes in the circadian activity rhythm of rats were observed when they were chronically treated with methamphetamine dissolved in drinking water. The circadian rhythm was phase-delayed with respect to the light-dark (LD) cycle, and showed signs of relative coordination. In some rats, the circadian organization was disturbed and two activity components appeared, with one component free-running and the other entrained by the LD cycle. After methamphetamine withdrawal, these changes disappeared rapidly but there were transient periods of 2-3 days before establishment of a stable entrainment to the LD cycle. The changes in the circadian rhythm persisted even in constant darkness (DD). The period around 24 hr in DD was significantly shorter during methamphetamine treatment than after the drug withdrawal. These results indicate that neither alteration of the sensitivity to light nor lengthening of the intrinsic period is involved in the methamphetamine induced disorganization of the circadian rhythm. Possible mechanisms are discussed in terms of a multi-oscillatory system.     

Circadian entrainment of the squirrel monkey by extreme photoperiods: Interactions between the phasic and tonic effects of light

To examine the role that the phasic and tonic aspects of the light-dark (LD) cycle play in entraining the circadian timing system of primates, squirrel monkeys (Saimiri sciureus) were exposed to 24 hr LD cycles in which the light duration (photoperiod) was varied from 1 sec to 23 hr. The monkeys were maintained in isolation and the circadian rhythm of drinking was monitored. The photoperiod was first gradually shortened until constant darkness was reached. Even in extremely short photoperiods of only one second of light per day, the drinking rhythm remained synchronized to the 24 hr period of the LD cycle. In the second set of experiments, the photoperiod was gradually lengthened until constant light was achieved. The drinking rhythm of all monkeys was synchronized by 21 hr photoperiods (LD 21:3), but free-ran in 23 hr photoperiods (LD 23:1) which provided a 1 hr dark pulse each day. The tonic effects of light may contribute to the difference between the ability to entrain to short versus long photoperiods. In constant darkness the free-running period was close to 24 hr, thus reducing the phase-resetting necessary to achieve entrainment to a 24 hr period by short light pulses. However, in constant light or in the long photoperiods which did not entrain (LD 23:1) the free-running period of the drinking rhythm was greater than 25 hr, thus requiring a much larger daily phase shift to achieve entrainment to a 24 hr period.     

Photoperiodic regulation of the time of birth in rats: involvement of circadian endogenous mechanisms

A resonance experiment was undertaken to demonstrate that photoperiod regulates birth time by endogenous circadian mechanisms. Pregnant rats were maintained on a standard light-dark (LD) cycle (14L-10D; lights on from 0600 to 2000 hr) or on fixed LD cycles with periods of 12, 24, 36 and 48 hours after day 8 of gestation. In these groups, the light phase (2 hr) started between 0600 and 0800 hr or between 1800 and 2000 hr illuminating exclusively (for periods of 24 and 48 hr) or alternatively (for periods of 12 and 36 hr) the hours corresponding to morning (M) or evening (E) of the standard light regimen. At the end of gestation, the general activity was manifested mainly at moments corresponding to the night of the standard regimen in most groups; it was delayed in the two groups lit up exclusively at E hours. In groups receiving light exclusively at M hours, birth times were delayed compared to the deliveries in groups receiving light at E hours only. An intermediate distribution of birth times was observed when M and E hours were stimulated every 12 hr but not every 36 hr. The apparent stability of the diurnal rhythm of activity and the difference in birth time distributions due to the period of light phase indicate that the regulation of birth time by photoperiod is due to a circadian mechanism in rats. This mechanism implicates at least two endogenous systems which are apparently antagonists with regard to birth.     

Feeding time synchronizes primate circadian rhythms.

Circadian rhythms of squirrel monkeys maintained in constant light and temperature can be entrained by 24 hr cycles of food availability with eating for 3 hr and fasting for 21 hr (EF 3:21). Rhythms of drinking, body temperature and urinary potassium and water excretion exhibited periods which matched the 24 hr period of the EF 3:21 cycle. These results suggest that temporal patterns of food intake are capable of synchronizing the circadian timekeeping system which underlies the observed rhythms.     

Fractional desynchronization of human circadian rhythms

Under the influence of artificial zeitgebers, human circadian rhythms can be entrained only within limited ranges of periods; different overt rhythms may show different entrainment limits. When the period of a zeitgeber is varied slowly but continuously, entrainment limits can be evaluated precisely. An overt rhythm is synchronized to the zeitgeber only up to a certain day, or period respectively, until it breaks away from the zeitgeber and starts to freerun. The interindividual comparison among different subjects shows that the range of entrainment is positioned nearly symmetrically around the freerunning period. Its width depends strongly on the freerunning period; it increases with lengthening freerunning period. As the consequence, subjects with a freerunning period only slightly shorter than 23 h would fail to become synchronized to the natural 24-h day, whereas subjects with a freerunning period even slightly longer 28 h would become synchronized. In the intraindividual comparison, overt rhythms of different variables show different entrainment limits. For instance, rhythms in urinary excretion of different electrolytes can be dissociated for several days; the same is true with the rhythms of deep body temperature and performance. This temporal separation excludes the possibility of functional interdependencies between the variables under consideration. Consequently, results obtained with this method of fractional desynchronization do not only assist in evaluating properties of the circadian system, but also assist in the search for physiological interconnections between different variables.     

Sex and ancestry determine the free‐running circadian period

The endogenous, free‐running circadian period (τ) determines the phase relationship that an organism assumes when entrained to the 24‐h day. We found a shorter circadian period in African Americans compared to non‐Hispanic European Americans (24.07 versus 24.33 h). We speculate that a short circadian period, closer to 24 h, was advantageous to humans living around the equator, but when humans migrated North out of Africa, where the photoperiod changes with seasons, natural selection favoured people with longer circadian periods. Recently, in evolutionary terms, immigrants came from Europe and Africa to America (‘the New World’). The Europeans were descendents of people who had lived in Europe for thousands of years with changing photoperiods (and presumably longer periods), whereas Africans had ancestors who had always lived around the equator (with shorter periods). It may have been advantageous to have a longer circadian period while living in Europe early in the evolution of humans. In our modern world, however, it is better to have a shorter period, because it helps make our circadian rhythms earlier, which is adaptive in our early‐bird‐dominated society. European American women had a shorter circadian period than men (24.24 versus 24.41), but there was no sex difference in African Americans (24.07 for both men and women). We speculate that selection pressures in Europe made men develop a slightly longer period than women to help them track dawn which could be useful for hunters, but less important for women as gatherers.     

Phase shifts of circadian rhythms in activity entrained to food access

Rats anticipate daily 2 hr meals with a sharp increase in activity several hours prior to food availability. The present experiment examined the response to phase shifts of food access in rats with lesions of the suprachiasmatic nuclei (SCN). Following entrainment of activity to 2 hr of food per day, food access was phase delayed or phase advanced by 4, 6, or 8 hr. All rats responded to phase delays of 4 or 6 hr with an increase in the duration of anticipatory activity so that transients appeared mostly in activity onset. Following 8 hr phase delays, clear delaying transients in both activity onset and end were observed. Only a few rats showed advancing transients in activity after phase advances of food access. In response to 6 hr and 8 hr phase advances, 3 different responses occurred: (a) activity re-entrained to food access by the 2nd or 3rd day without clear intervening transients, (b) activity phase shifted by means of distinct delaying transients and (c) delaying transients occurred in one component of activity while a second component of activity appeared at the new phase position by the second or third day. These results provide further evidence that anticipation of food access is mediated by a circadian mechanism which is functionally independent of the SCN and illustrate some similarities as well as considerable differences between circadian rhythms entrained by feeding and those entrained by light-dark cycles.     

Periodic exposure to mother is potent zeitgeber of rat pups' rhythm

To study the possibility and potency of periodic maternal deprivation (PMD) in entraining the circadian rhythm of rat pups, access to the natural mother of which pups were optically enucleated on the day of birth (day 1) was restricted to either light phase (L-group) or dark phase (D-group) for various durations beginning on various days during the nursing period. Drinking rhythm of both groups was determined once per one or two weeks between the 4th and 8th postnatal week. The corticosterone rhythm was determined to confirm the results obtained by the measurement of water intake. Both rhythms were clearly observed by 5 weeks of age, and a reversed phase relationship was observed even when PMD was performed for a short period during days 1-4 or days 15-21. On the other hand, no phase angle difference was observed between L- and D-groups, when pups were periodically exposed to their original mother either during days 1-2 or days 18-21. These facts indicate that periodic exposure to mother can set the phase of the blinded pups' rhythm and that the period required for entrainment of the rhythm is as short as 4 or 7 days in the early or late times during the nursing period respectively, showing the high potency of PMD in entraining the circadian rhythm of blinded pups.     

Relations between muricide, circadian rhythm and consummatory behavior

Three forms of behavior--muricide, eating, and drinking--have been studied at six photic periods during a 12/12 hr light/dark circadian cycle to which the subjects have been habituated. One hundred and eight rats served as subjects, 18 per photic period. The frequency of muricide was recorded for each period and subsequent food and water intakes were measured during a 1 hr test period. Results show a significantly higher frequency of muricide during the dark than during periods of light. Food intake covaried significantly with the incidence of muricide rs = 0.89, p less than 0.05), while no such relationship was found between muricide and water intake (rs = 0.17, p less than 0.05). The findings are consistent with reports of circadian changes in other rodent behaviors, including rhythmicity in home-cage and in shock-induced aggression. Covariation of muricide and eating does not establish a causal relation between the two. Three models of physiological mechanisms which might provide substrates for the covariance are discussed.     

Circadian modification of ethanol damage in utero to mice

This study evaluates the ethanol toxicity for fetal development at different circadian stages. Pregnant mice were given a single intraperitoneal ethanol injection on day 7, 8, or 10 of gestation at one of four circadian stages (0700, 1300, 1900, or 0100 hr). The dams were killed on the day before term (day 18). Prenatal exposure to ethanol resulted in an increased number of resorptions, reduced fetal body weight, and produced an increased incidence of external alterations. The severity of damage was related to the dose, the period of gestation, and particularly to the circadian stage at the time of treatment. Ethanol had the greatest effect on the embryo of a mouse when administered at the mid-dark span. Consequently exposure to a single dose of ethanol at one time or another along the 24-hr time scale during organogenesis has important implications for the substantially increased risk.     

Patterns of daily physical activity during school days in children and adolescents

The purpose of this study was to examine the weekday patterns of moderate‐to‐vigorous physical activity (MVPA) in school children and adolescents and determine if there are periods of the day that are representative of their typical MVPA. The sample comprised 84 subjects (boys, n = 30; girls, n = 54), age 8–15 years old. Daily totals for the physical activity variables were calculated by summing the values from 13hr of physical activity (PA) measurements (9:00–22:00), with 60‐min time blocks comprising each day. The MVPA data values were categorized in four daily periods: morning (9:00–11:59), noon (12:00–14:59), late afternoon (15:00–17.59), and evening (18:00–21.59). Our data show that boys participated significantly more in MVPA than girls. Despite no clear patterns or differences among sex being found, girls showed higher percent of time engaged in MVPA during the morning and early afternoon periods (sum of two periods 51.0%), while boys' percent of time engaged in MVPA is higher at late afternoon and evening periods (sum of two periods 53.8%). The principal components analyses showed four distinct components that accounted for 67% of the variance, as follows: school hours (component 1); lunchtime and outside‐school activities (component 2); morning time before school period (component 4); and period before bedtime (component 3) appear as distinct periods of the day. In conclusion, the present study shows that boys engaged more in MVPA than girls. Girls tend to be more active during school periods, while boys are more active after school. Am. J. Hum. Biol. 15:547–553, 2003. © 2003 Wiley‐Liss, Inc.     

Duration and Placement of Sleep in a "Disentrained" Environment

Sleep/wake cycles of 9 young adults were electrographically recorded during 60 hrs of enforced bedrest. During this period subjects were required to lie quietly, with no time cues and minimal exogenous stimulation. Sleep and wakefulness patterns were clearly modified under these conditions. There was an alternation of waking periods with an average length of 2.7 hrs and sleep episodes with a mean duration of 2.99 hrs. Eighty percent of both sleep and waking periods were less than 4 hrs duration. The circadian pattern of sleep period duration persisted in disentrainment, but temporal organization of sleep episodes was substantially disrupted; sleep episodes occurred throughout the 24-hr day. The results suggest the presence of two distinct components of the human sleep system–one, sleep duration, is controlled by an endogenous circadian oscillatory system; another, sleep placement, is controlled primarily by behavioral controls, in the form of social and occupational pressures, and self-imposed behavioral alternatives to sleep.     

Natural light exposure of young adults

Bright light has a role in natural coordination of mammalian circadian and seasonal rhythms. In humans, the light intensity must probably exceed 2000 lux to be optimal. Natural light exposures of 10 healthy adults were measured over a 24-hour period, using forehead illumination transducers connected to a portable computer. The subjects varied markedly in duration and timing of exposures to light greater than 2000 lux. On average, the subjects experienced bright light for only 90 minutes per day, less than the 3-8 hours of bright light necessary to maximally synchronize human circadian rhythms. These results suggest that natural and artificial light exposure for many Americans may be suboptimal for circadian and seasonal synchronization.     

Circadian rhythm of luminance detectability in the rat

Rats lived in a visual detection test environment which allowed for around-the-clock measurement of the detectability of a 500 nm stimulus of low luminance. Daily trends in visual sensitivity were compared with a behavioral activity measure, the rate of trial initiations in the self-paced testing procedure. Both variables showed circadian rhythms with periods exceeding 24 hr in the absence of day-night cues. However, the two oscillations were phase-displaced, such that maximal visual sensitivity occurred earlier than did maximal behavioral activity, each day. The temporal organization of visual sensitivity may underlie well-known photic influence on circadian rhythms and photoperiodic behavior.     

The 24-h growth hormone rhythm in men: sleep and circadian influences questioned

The 24-h rhythm of growth hormone (GH) is thought to be controlled primarily by sleep processes with a weak circadian component. This concept has been recently questioned in sleep-deprived persons. To test the notion of a high sleep-dependency of GH release, we established simultaneous 24-h rhythms of GH and melatonin, a circadian marker, in night workers who form a model for challenging sleep and circadian processes. Ten day-active subjects and 11 night workers were studied during their usual sleep-wake schedule, with sleep from 23:00 to 07:00 hours and 07:00 to 15:00 hours, respectively. Experiments were conducted in sleep rooms under continuous nutrition, bed rest, and dim light. Melatonin and GH were measured every 10 min over 24 h. In day-active subjects, melatonin and GH showed the well-known 24-h profiles, with a major sleep-related GH pulse accounting for 52.8 +/- 3.5% of the 24-h GH production and the onset of the melatonin surge occurring at 21:53 hours +/- 18 min. In night workers, melatonin showed variable circadian adaptation, with the onset of secretion varying between 21:45 and 05:05 hours. The sleep-related GH pulse was lowered, but the reduction was compensated for by the emergence of large individual pulses occurring unpredictably during waking periods, so that the total amount of GH secreted during the 24 h was constant. One cannot predict the degree of GH adaptation from the highly variable melatonin shift. These results argue against the concept that sleep processes exert a predominant influence on GH release whatever the conditions. When sleep and circadian processes are misaligned, the blunting of the sleep-related GH pulse is counteracted, as in sleep-deprived persons, by a compensatory mechanism promoting GH pulses during wakefulness.     

Ovulation,Fertilization, and Early Embryonic Development in the Menstruating Fruit Bat,Carollia perspicillata

To characterize periovulatory events, reproductive tracts were collected at 12 hr intervals from captive‐bred, short‐tailed fruit bats, Carollia perspicillata, on days 1–3 post coitum and examined histologically. Most bats bred readily. Graafian follicles developed large antra and exhibited preovulatory expansion of the cumulus oophorus. Ovulation had occurred in some on the morning, and in most by the evening, of day 1. The single ovum was released as a secondary oocyte and fertilized in the oviductal ampulla. Ovulated secondary oocytes were loosely associated with their cumulus cells, which were lost around the initiation of fertilization. Supernumerary spermatozoa were occasionally noted attached to the zonae pellucidae of oviductal ova, but never within the perivitelline space. By day 2, most ova had reached the pronuclear stage and by day 3, early cleavage stages. Several lines of evidence indicate that C. perspicillata is a spontaneous ovulator with a functional luteal phase. Most newly mated females had recently formed, but regressing corpora lutea, and thickened (albeit menstrual) uteri despite having been housed with males only for brief periods (<23 days). Menstruation is usually periovulatory in this species. Furthermore, the interval between successive estrus periods in most mated females that failed to establish ongoing pregnancies at the first was 21–27 days. Menstruation involved substantial endometrial desquamation, plus associated bleeding, and generally extended to the evening of day 3, the last time point studied. In nearly all females with a recent corpus luteum (n = 24 of 25; 96%), the preovulatory or newly ruptured follicle was in the opposite ovary. Anat Rec, 2011. © 2010 Wiley‐Liss, Inc.     

Control of the rat's circadian self-stimulation rhythm by light-dark cycles.

Rats with hypothalamic and septal electrodes were maintained in continuous test environments where bar-press responses produced brief reinforcing electrical stimulations. Long-term trends in response emission were measured under continuous exposure to light, dark and 12 hr light-dark alternations. In addition, transient behavioral adjustment to sudden 180 degrees phase shifts in the light-dark schedule was studied. The ambient light condition was found to control the period and phase of the circadian rhythm of brain self-stimulation behavior, as quantified by Fourier analysis. The circadian period was greatest under constant light (up to 24.90 hr under dim illumination), and approximated 24.00 hr under constant dark. Successful nocturnal entrainment to 12 hr light-dark alternations was obtained, with the peak of the 24 hr Fourier fundamental occurring in the middle-to-late dark segments. Three to 11 days were required for re-entrainment to 180 degrees light-dark phase shifts, during which the behavioral oscillation period increased to values comparable to periods under constant light. The rate of re-entrainment appeared to be proportional to illumination intensity during light segments.     

早产儿的循环,呼吸和体温的多成份生物节律

生物节律是多成分的节律系统,但是,几乎没有人报道关于新生儿的不同成分(频率)的生物节律之间的关系。本研究,对21位早产儿出生后第一星期内的血压,心率,呼吸,血氧饱和度和体温作了多频率的时间生物学变化特点做了研究。分别用周期是7天,1天的余弦函数去拟合上述变量。结果是在早产儿出生以后生命的第一星期内,全部早产儿的上述这些变量的生物节律特征是以七日节律出现明显地多于近日节律。这一结果提示了在生命的早期阶段,机体的生物节律以低频率的生物节律是生物节律的主要成分,这对研究生物节律的起源有着重要的意义。     

The development of infants' circadian rest-activity rhythm and mothers' rhythm

In order to know when and how infants obtain their circadian sleep-wake rhythm, infants' developing circadian rest-activity rhythm and mothers' circadian rhythm in the postpartum period were examined using actigraph monitoring. The subjects were 11 primipara and their infants. Actigraphic recordings for the infants and their mothers were made over 3-5 continuous days during the 3rd, 6th, 9th and 12th weeks after birth. A 24-h peak on a mean autocorrelogram of the infants' movements was detected at the 3rd week. The infants' circadian rest-activity rhythm already existed in the 3rd week. The amplitude of this 24-h peak gradually increased from the 6th to 12th week. This may be useful as an index of the development of infants' circadian rest-activity rhythm. An 11-h peak was also observed at the 3rd week. This 11-h peak was thought to be a semi-circadian rhythm. Regarding the mothers, the amplitude of the 24-h peak on the mean autocorrelogram at the 3rd week was the smallest of all other weeks, and it became larger from the 3rd to 12th week. This meant that the mothers' circadian rhythm at the 3rd week was influenced by their interrupted sleep at night to take care of their infants. The mother-infant synchronization is probably the 1st factor in the entrainment of infants' circadian sleep-wake rhythm. In this study, we also propose a novel method for compensating for missing data in autocorrelogram analysis.     

Direct and circadian control of sparrow behavior by light and dark

House sparrows, Passer domesticus, have perch-hopping activity (1) which was elicited by light (direct), and (2) which exhibited daily rhythms that were entrained by environmental light-dark cycles (circadian). When photoperiod was more than 14 hr, the sparrows' activity coincided with the light; when it was less than 14 hr, the birds were also active in the dark according to circadian predictions. Bimodality was dependent on photoperiod with the maximum incidence (75%) in LD16:8. Sparrows placed in LD1:11 (skeleton of 13:11) synchronized the onsets of their activity with the light beginning 8-18 hr after the time of the last L/D irrespective of when the birds experienced the first 1 hr light. Thirty-five percent of the sparrows advanced when they entrained to LD1:11 with the first pulse 8 hr after the last L/D; 76-87% of the sparrows delayed when they entrained to LD1:11 with the first pulse 2, 5 or 18 after the last L/D. Sparrows kept in exotic light-dark cycles (with periods of 10 min, 1.5 hr, 3.0 hr, 6.0 hr, 12 hr) were active in the light. Some birds displayed circadian rhythms superimposed on short period patterns. The period lengths of the circadian rhythms were shorter (22.8 hr) than in constant dark (24.2 hr). When sparrows subjected to LD1.5:1.5 or 36 hr of constant light were placed in constant dark, the phase of their activity onsets extrapolated to 15 hr after the last lights-off.