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Restricted feeding during the resting period causes pronounced shifts in a number of peripheral clocks, but not the central clock in the suprachiasmatic nucleus (SCN). By contrast, daily caloric restriction impacts also the light-entrained SCN clock, as indicated by shifted oscillations of clock (PER1) and clock-controlled (vasopressin) proteins. To determine if these SCN changes are due to the metabolic or timing cues of the restricted feeding, mice were challenged with an ultradian 6-meals schedule (1 food access every 4 h) to abolish the daily periodicity of feeding. Mice fed with ultradian feeding that lost <10% body mass (i.e. isocaloric) displayed 1.5-h phase-advance of body temperature rhythm, but remained mostly nocturnal, together with up-regulated vasopressin and down-regulated PER1 and PER2 levels in the SCN. Hepatic expression of clock genes (Per2, Rev-erbα, andClock) andFgf21was, respectively, phase-advanced and up-regulated by ultradian feeding. Mice fed with ultradian feeding that lost >10% body mass (i.e. hypocaloric) became more diurnal, hypothermic in late night, and displayed larger (3.5 h) advance of body temperature rhythm, more reduced PER1 expression in the SCN, and further modified gene expression in the liver (e.g. larger phase-advance ofPer2and up-regulated levels ofPgc-1α). While glucose rhythmicity was lost under ultradian feeding, the phase of daily rhythms in liver glycogen and plasma corticosterone (albeit increased in amplitude) remained unchanged. In conclusion, the additional impact of hypocaloric conditions on the SCN are mainly due to the metabolic and not the timing effects of restricted daytime feeding. [ABSTRACT FROM PUBLISHER]

The aim of this study was to examine the ultradian dynamic of emotional processing in men. Event-related potentials were recorded while participants watched different sets of unpleasant and neutral pictures every 15 min for 3 h. Emotional feelings induced by unpleasant pictures were also assessed with self-rating scales at the end of each picture set. Whereas brain processing of neutral pictures remained stable over time, a late positive component elicited by unpleasant pictures presented ultradian oscillations varying between 65 and 110 min in 77% of the participants, mainly in the right centro-posterior area. Ultradian rhythms were also observed for values self-rating the intensity of unpleasant feelings. Correlative analyses performed between brain and behavioral ultradian oscillations indicated that these rhythms follow a temporal opposite pattern. For the first time, these results raise questions regarding the modulating role of ultradian oscillations when the brain computes the significance of unpleasant stimuli and produces the final emotional feelings. Overall, these findings open new perspectives on the temporal regulation of emotional reactivity in healthy individuals and in those with affective disorders. [ABSTRACT FROM AUTHOR]

The aim of the present study was to evaluate the development of the circadian rhythm of the salivary cortisol in premature infants and its correlation with the onset of the sleep-activity behavior pattern during the first 3 weeks of life under controlled light:dark conditions. Furthermore, we investigated the influence of acoustic stimulation by audiotaped lullabies or the maternal voice on the cortisol values and long-term sleep-activity patterns. The study was a block-randomized, prospective clinical trial with a study population of 62 preterm neonates (30 < 37 gestational age). We compared two study groups who listened either to music or to the maternal voice (music: N = 20; maternal voice: N = 20) with a matched control group ( N = 22). The acoustic stimulation took place every evening between 20:00 and 21:00 h for 30 min over a period of 2 weeks. The cortisol values and activity-rest behavior of the neonates were determined during the first 3 weeks of life on the 1st, 7th and 14th day. Actigraphic monitoring was used to record the activity pattern continuously over 24 h and a validated algorithm for neonates was used to estimate sleep and wakefulness. The saliva samples were obtained 10 min before and 10 min after the acoustic interventions for the study groups. Additionally, saliva samples were obtained from the control group seven times over a 24-h period (20:00, 21:00, 01:00, 05:00, 08:00, 13:00 and 17:00 h). The cortisol data were analyzed by fast Fourier transformation to assess periodic characteristics and frequencies. Hierarchical linear modeling was further performed for the statistical analysis. Results: The cortisol rhythm analysis indicated a circadian rhythm pattern for only one premature infant, all others of the neonates showed no circadian or ultradian rhythm in cortisol. Cortisol level of the premature neonates was significantly higher during the first day of the study period at night-time (median: 17.1 nmol/L, IQR = 9.7-24.4 nmol/L) than on days 7 (median: 9.6 nmol/L, IQR = 4.7-14.6 nmol/L; Tukey-HSD, z = 4.12, p < 0.001) and 14 (IQR = 5.8-13.7 nmol/L; Tukey-HSD, z = 2.89, p < 0.05). No significant effect of acoustic stimulation was observed on the cortisol concentration and sleep-wake behavior. The activity-sleep rhythm of preterm neonates was dominated by ultradian rhythm patterns with a prominent period length of 4 h (30.5%). Activity frequencies of neonates were also significantly higher overnight on the first study day (mean: 329 ± 185.1 U) than of night seven (mean: 260.2 ± 132.4 U; Tukey-HSD, z = 2.50, p < 0.05). Quiet-activity patterns increased, whereas high-activity patterns decreased during the observation period. Average sleep time increased significantly during the study time from day 1 to day 7 (Tukey-HSD, z = 2.51, p < 0.05). In conclusion, premature infants showed higher cortisol levels - without a circadian rhythmicity - and higher activity frequencies in the first days after birth which may reflect an adaptation process of neonates after birth. Cortisol concentrations and the activity patterns were not influenced by music interventions. [ABSTRACT FROM AUTHOR]

Ultradian rhythms, such as sleep-wake periodicities, during the night might represent basic rest-activity cycles of organisms that are fundamental to the temporal organization and synchronization of behavior throughout the day. However, in contrast to circadian rhythms, little is known about the underlying oscillators and molecular mechanisms of higher-frequency rhythms. A fundamental step for the understanding of the mechanisms of these latter periodicities is the analysis of variation in sleep-wake cycles in free-living animals, which can help in estimating the relative importance of genetic and environmental influence on the rhythmicity. We analyzed variation in the level of rhythmicity and period length (τ) of behaviorally defined sleep-wake cycles in a natural population of blue tits Cyanistes caeruleus. Our results indicate that the expression of periodicity in sleep-wake patterns, but not τ, has a strong individual-specific basis. The within-individual repeatability estimate of the expression of periodicity was .45 (95% confidence interval: .35-.55) when data from males and females were combined. In addition, periodicity was influenced by specific environmental factors, such as night temperature, seasonal date, and age of the individual. Most strikingly, low nighttime temperature negatively affected periodicity of sleep-wake patterns, potentially via a hypothermic response of the birds. Our results further suggest that τ is influenced by photoperiod. Blue tits showed longer sleep-wake rhythms when the nights were longer. These observations suggest a genetic basis for the incidence of rhythmic sleep-wake behavior in addition to environmental modifications of their specific expression. (Author correspondence: ) [ABSTRACT FROM AUTHOR]

Light is the main entraining signal of the central circadian clock, which drives circadian organization of activity. When food is made available during only certain parts of the day, it can entrain the clock in the liver without changing the phase of the central circadian clock. Although a hallmark of food entrainment is a behavioral anticipation of food availability, the extent of behavioral alterations in response to food availability has not been fully characterized. The authors have investigated interactions between light and temporal food availability in the timing of activity in the common vole. Temporally restricted food availability enhanced or attenuated re-entrainment to a phase advance in light entrainment when it was shifted together with the light or remained at the same time of day, respectively. When light-entrained behavior was challenged with temporal food availability cycles with a different period, two distinct activity components were observed. More so, the present data indicate that in the presence of cycles of different period length of food and light, an activity component emerged that appeared to be driven by a free-running (light-entrainable) clock. Because the authors have previously shown that in the common vole altering activity through running-wheel availability can alter the effectiveness of food availability to entrain the clock in the liver, the authors included running-wheel availability as a parameter that alters the circadian//ultradian balance in activity. In the current protocols, running-wheel availability enhanced the entraining potential of both light and food availability in a differential way. The data presented here show that in the vole activity is a complex of individually driven components and that this activity is, itself, an important modulator of the effectiveness of entraining signals such as light and food. (Author correspondence: ) [ABSTRACT FROM AUTHOR]

Sleep-wake regulation involves reciprocal interactions between sleep- and wake-promoting processes that inhibit one another. To uncover the signatures of the opponent processes underlying ultradian sleep cycles, principal component analysis was performed on the sets of 16 single-Hz log-transformed electroencephalographic (EEG) power densities (1--16 Hz frequency range). Data were collected during unrestricted night sleep followed by 9 20-min naps (14 women aged 17--55 yrs) and during 12 20-min naps after either restriction or deprivation of sleep (9 males and 9 males, respectively, aged 18--22 yrs). It was found that any subset of power spectra could be reduced to the invariant four--principal component structure. The time courses of scores on these four components might be interpreted as the spectral EEG markers of the kinetics of two pairs of opponent chronoregulatory processes. In a sequence of ultradian sleep cycles, the 1st and 2nd components represent the alternations between competing drives for sleep and wakefulness, respectively, whereas the 3rd and 4th components reflect the alternations between light and deep sleep, respectively. The results suggest that principal component structuring of EEG spectrum can be employed for derivation of the parameters of the quantitative models conceptualizing the three major aspects of sleep-wake regulation--homeostatic, circadian, and ultradian processes. (Author correspondence: ) [ABSTRACT FROM AUTHOR]

Subterranean common mole voles, Ellobius talpinus, were implanted with long-term recording electronic thermometers to obtain hourly body temperature (Tb) data during either the wintertime or summertime. The two individuals tested during the summertime had significant circadian and ultradian rhythms in their Tb. Four of the five mole voles tested during the wintertime lacked rhythmicity in their Tb. The fifth individual lacked circadian rhythms but had ultradian rhythms in its Tb. A loss of circadian rhythms in Tb during deep torpor or hibernation has been reported for a few species of mammals. Inasmuch as the mole voles' wintertime Tb remained at euthermic levels, our results show that a loss of circadian body temperature rhythms in mole voles does not require the low Tb of deep torpor or hibernation. A tentative conclusion, based on these few animals, is that in common mole voles the Tb rhythms may disappear during the wintertime even though their Tb remains high. (Author correspondence: ) [ABSTRACT FROM AUTHOR]

The effects of different photophase irradiance levels on the daily rhythms of energy expenditure (DEE, calculated from oxygen consumption, VO2) and urinary metabolites of stress hormones in sighted ( Microtus socialis) and blind ( Spalax ehrenbergi) rodents were compared. Five groups of each species were exposed to different irradiance levels (73, 147, 293, 366, and 498 μW/cm2) under short photoperiod (8L:16D) condition with constant ambient temperature 25 ± 2°C for 21 days before assessments. As light intensity increased from 73 μW/cm2, both species reduced DEE, especially among M. socialis. Cosinor analysis revealed significant ultradian rhythms in VO2 of M. socialis with period length being inversely related to irradiance level. Conversely, in S. ehrenbergi, robust 24 h VO2 rhythms were detected at all irradiances. In M. socialis, significant 24 h rhythms in urinary output of adrenaline were detected only at 293 μW/cm2, whereas for cortisol, unambiguous rhythms were detected at 73 and 147 μW/cm2. Distinct adrenaline daily rhythms of S. ehrenbergi were observed at 73 and 293 μW/cm2, whereas this species exhibited significant rhythms in cortisol at 147 and 293 μW/cm2. Changes in photophase irradiance levels affected stress hormone concentrations in a dose-dependent manner. There were significant negative and positive correlations of M. socialis and S. ehrenbergi stress hormones, respectively, with increasing irradiance. Our results indicate photophase light intensity is another environmental factor that can significantly affect entrainment of mammalian daily rhythms. Both low and high irradiance conditions can trigger stress responses, depending on the species' natural habitat. (Author correspondence: zubidat3@013.net.il) [ABSTRACT FROM AUTHOR]

24 h and ultradian rhythms of blood pressure (BP) have been previously shown to be disorganized in nocturnal hypertensive subjects. The present study was undertaken to further analyze the ultradian and circadian BP rhythm structure in sleep-time hypertensive subjects with normal or elevated awake-time BP levels. Fourier analysis was used to fit 24, 12, 8, and 6 h curves to mean BP as well as heart rate (HR) time series data derived from 24 h ambulatory blood pressure monitoring. Awake and sleep periods were defined according to individual sleep diaries. Awake-time hypertension was defined as diurnal systolic (SBP) and/or diastolic BP (DBP) means ≥135/85 mmHg. Sleep-time hypertension was defined as nocturnal SBP and/or DBP means ≥120/70 mmHg. The sample included 240 awake-time normotensive subjects (180 sleep-time normotensives and 60 sleep-time hypertensives) and 138 untreated awake-time hypertensive subjects (31 sleep-time normotensives and 107 sleep-time hypertensives). The amplitude and integrity (i.e., percent rhythm) of the 24 and 12 h BP rhythms were lower in the sleep-time hypertensive subjects and higher in the awake-time hypertensive subjects. However, no differences were detected when the integrity and amplitude of the 6 and 8 h mean BP rhythms were analyzed. The sleep-time hypertensive group showed significantly higher 24 h BP rhythm acrophase variability. No differences could be found in any of the HR rhythm parameters. Altogether, the findings suggest a disorganization of the BP circadian rhythm in sleep-time hypertensives that results in reduced 24 h rhythm amplitude and integrity that could be related to cardiovascular risk. [ABSTRACT FROM AUTHOR]

The molecular clock machinery in mammals consists of a number of clock genes (CGs) and their resultant proteins that form interlocking transcription-translation feedback loops. These loops generate and maintain the 24 h mRNA and protein oscillations and consequential biological and physiological rhythms. To understand whether peripheral oscillators share similarly-timed clock machinery, the temporal expression patterns of the seven recognized key CGs (mPer1, mPer2, mCry1, mCry2, mRev-erb alpha, mClock, and mBmal1) were examined simultaneously in six peripheral tissues in mice every 4 h for 24 h in synchronized light-dark conditions using real time PCR assays. Time series were analyzed for time-effect by ANOVA and for rhythm characteristics by the single cosinor fitting procedure. The expression levels of most CGs were comparable in liver, kidney, and spleen, but mBmal1 and mCry1 were more abundant in the thymus, and mPer1, mCry1, and mCry2 were more abundant in the testis. In addition, mCry2 was dramatically lower in the kidney, spleen, and thymus; mPer2 was significantly lower in the spleen, testis, and thymus; and all of the genes tested were strikingly less abundant in peripheral blood. A significant 24 h rhythmic component was found for each CG in the liver and kidney and for some CGs in other tissues. Of note, a 12 h ultradian rhythmic component was also found in mRNA expression for some CGs in several of the tissues and was the only significant oscillation observed for CGs in the testis. Ultradian oscillations were also observed for mPer1 in the testis (8 h) and thymus (12 h and 8 h) in a second study where mice were sampled every 2 h. The present results suggest that the functioning of the molecular circadian clock may be modified to some extent between peripheral tissues, as denoted by differences in amplitude and phasing, and operates differently or is less developed in tissues containing differentiating cells (i.e., testis and thymus), as denoted by the presence of ultradian patterns resulting in two or more peaks within 24 h. [ABSTRACT FROM AUTHOR]

Daily changes in cognitive performance have been documented, both in time of day/effect paradigm studies and in time‐isolation studies. However, in both types of studies, phenomena such as the “post‐lunch dip” have been found that were difficult to explain in terms of theoretical backgrounds. These phenomena may suggest ultradian rhythms in cognitive performance. A number of studies have also shown ultradian and asymmetric rhythms in activity indices of the brain hemispheres. The aim of this study was to test three hypotheses: the first two assumed that there is a significant ultradian frequency in a component of the endogenous rhythm of processing speed, and the third assumed that the ultradian endogenous rhythms of the processing speed (encoding and recognition) of stimuli addressed to the left brain hemisphere differ in period length from those addressed to right hemisphere. During a 24 h constant‐routine experiment, the memory performance of 30 participants was measured eight times (every 2.5–3 h), starting at 06:30 h. Parallel sets of words and pictures were shown to subjects in a random order in either the left or the right visual field on a computer screen. The participants pressed one of two buttons in response to the picture or word, or when answering a question concerning the meaning of a presented stimulus. Cosinor analysis was applied to individual time series data. Two significant ultradian components were found in a majority of the time series. Dominant periods were analyzed using three factor ANOVA. The results showed an asymmetry between both hemispheres in the frequency of ultradian rhythms in encoding speed. [ABSTRACT FROM AUTHOR]

The focus of this study was on daytime and nighttime sleep and wakefulness during the peak age for Sudden Infant Death Syndrome (SIDS), two to four months, to determine whether there are differences between at‐risk for SIDS (R) and control (C) infants. Such differences may provide insight on the frequent occurrence of SIDS in the early morning hours, when most babies are asleep. This is the only study in which R and C infants were continuously monitored for long periods of time (24–48 h) and then followed and recorded at monthly intervals until the age of 4–6 months. Data analyses indicate that ultradian REM/NREM cyclicity becomes stabilized into a regular pattern at three months of age. Infants at this age convert from a polyphasic sleep/wakefulness pattern to a circadian one. Among the changes that occur is a lengthening of short sleep periods that consolidate at night and wake periods that consolidate in the daytime. The most striking effects are related to sleep state and vary according to age and sex. The lengthening of single sleep and wakeful periods is coupled with the maturation of the brain. The development of the central nervous system facilitates the synchronization of sleeping patterns with external light input and social entrainment. One or more biological clocks or oscillators may be responsible for these REM/NREM patterns and circadian cycles. These differences during the early morning hours, when the occurrence of SIDS peaks, may have important implications for understanding the pathophysiological mechanism of SIDS. [ABSTRACT FROM AUTHOR]

Thiosulfate sulfurtransferase (TST) is an important ‘enzyme of protection,’ that accelerates the detoxification of cyanide, converting it into thiocyanate. The TST physiological rhythm was investigated at wks 2, 4, and 8 of post‐natal development (PND) in the mouse. The results revealed a statistically significant gender‐related difference, with the highest activity in females, at all the documented PND stages. In the second week of PND (pre‐weaning time), the circadian rhythm of the enzyme activity was associated with ultradian components. The prominent circadian rhythm (τ=24 h) peaked at the beginning of the light span, more precisely &nvsim;3 HALO (Hours After Light Onset). A week after weaning (wk 4 of PND), an impairment of the rhythm, with the peak shifted toward the second half of photophase, was recorded. Four to 6 wks later, about wk 8 of PND, the circadian rhythm pattern was stabilized, with its peak then located at the beginning of the dark span (13 HALO). The obtained results showed a 12 h phase‐shift of the circadian TST peak time during PND, suggesting that the rhythm stabilization is age‐dependent. [ABSTRACT FROM AUTHOR]

Periodogram techniques on detrended data were used to determine the incidence of Trypanosoma brucei brucei infection on the distribution of the core temperature of rats and the expression of temperature rhythms. In such an animal model, sudden episodic hypothermic bouts were described. These episodes of hypothermia are used here as temporal marks for the purpose of performing punctual comparisons on temperature organization. The experiment was conducted on 10 infected and 3 control Sprague‐Dawley rats reared under a 24 h light‐dark cycle. Core temperature was recorded continuously throughout the experiment, until the animals' death. Temperature distributions, analyzed longitudinally across the full duration of the experiment, exhibited a progressive shift from a bimodal to unimodal pattern, suggesting a weakening of the day/night core temperature differences. After hypothermic events, the robustness of the circadian rhythm substantially weakened, also affecting the ultradian components. The ultradian periods were reduced, suggesting fragmentation of temperature generation. Moreover, differences between daytime and nighttime ultradian patterns decreased during illness, confirming the weakening of the circadian component. The results of the experiments show that both core temperature distribution and temperature rhythm were disrupted during the infection. These disruptions worsened after each episode of hypothermia, suggesting an alteration of the temperature regulatory system. [ABSTRACT FROM AUTHOR]

In healthy mature subjects simple reaction time (SRT) to a single light signal (an easy task) is associated with a prominent rhythm with τ = 24h of dominant (DH) as well as nondominant (NDH) hand performance, while three-choice reaction time (CRT), a complex task, is associated with τ = 24 h of the DH but τ < 24 h of the NDH. The aims of the study were to assess the influence of age and gender on the difference in r of the NDH and DH, as it relates to the corresponding cortical hemisphere of the brain, in comparison to the rhythm in handgrip strength. Healthy subjects, 9 (5 M and 4 F) adolescents 10-16 yr of age and 15 (8 M and 7 F) adults 18-67 yr of age, active between 08: 00 ± 1 h and 23: 00 ± 1: 30 h and free of alcohol, tobacco, and drug consumption volunteered. Data were gathered longitudinally at home and work 4-7 times daily for 11-20 d. At each test time the following variables were assessed: grip strength of both hands (Dynamometer: Colin-Gentile, Paris, France); single reaction time to a yellow signal (SRT); and CRT to randomized yellow, red, or green signal series with varying instruction from test to test (Psycholog-24: Biophyderm, France). Rhythms in the performance in SRT, CRT, and handgrip strength of both DH and NDH were explored. The sleep-wake rhythm was assessed by sleep-logs, and in a subset of 14 subjects it was also assessed by wrist actigraphy (Mini-Motionlogger: AMI, Ardsley NY). Exploration of the prominent period r of time series was achieved by a special power spectra analysis for unequally spaced data. Cosinor analysis was used to quantify the rhythm amplitude A and rhythm-adjusted mean M of the power spectral analysis determined trial τ. A 24h sleep-wake rhythm was detected in almost all cases. In adults, a prominent r of 24 h characterized the performance of the easy task by both the DH and NDH. In adults a prominent r of 24 h was also detected in the complex CRT task performed by the DH, but for the... [ABSTRACT FROM AUTHOR]

The aim of this study was to determine whether the presence of a maternal hen influences the quality, quantity, and distribution of activity in young chicks. Brooded and nonbrooded chicks were observed during the entire light phase when they were 4 d of age. Our results revealed that although both brooded and nonbrooded chicks expressed the same behavioral items and in quite the same quantity, activity bouts were much longer in brooded chicks. However, only brooded chicks presented a high level of ultradian rhythmicity. Moreover, the brooded chicks made greater use of the space. The presence and the behavior of maternal hens appeared to provide structuring factors for the expression of the chicks' behavior. [ABSTRACT FROM AUTHOR]

To provide necessary background for study of stress response in redbacked voles (Clethrionomys gapperi), the circadian and ultradian rhythm in corticosterone release was characterized. Animals were maintained under a 16h light, 8h dark cycle. A total of 55 males and 46 females provided 101 independent blood samples over a 6-month span. Samples were obtained at 1h to 2h intervals during the light and at 2h intervals during the dark. Using edited data (5 values beyond the upper 95% limit were removed), a significant time effect was found by analysis of variance (ANOVA) for both sexes at P < .001. The composite single cosine best describing the circadian waveform for each sex consisted of three components (24h, 12h, and 6h), each significant at P < .05 (overall model P < .001). The 24h mean (mesor) was about 60% higher in females than males (646 ng/mL vs. 412 ng/mL, P = .01), with amplitudes of 429 and 298 ng/mL being proportional (66% vs. 72%) to the respective mesor. The predictable range of change within a 24h span (determined by the double amplitude of a 24h + 12h + 6h cosine model) was large: It was more than 1600 ng/mL for females and more than 900 ng/mL for males. Highest values were found during the dark phase, with the 24h acrophase located at 2h into the dark span for both sexes. With the caveat of fewer samples obtained during dark than during light, the actual peak values for females occurred at 2h and for males at 6h into the 8h dark span. These results provide baseline information about the circadian time structure for serum corticosterone in red-backed voles under normal light-dark, lowstress conditions. (Chronobiology International 18(6) 933–945, 2001) [ABSTRACT FROM AUTHOR]

Studies suggest some physiologic, cognitive, and behavioral 24h rhythms are generated by cyclic components that are shorter in period than circadian. The aim of this study was () to examine the hypothesis that 24h human performance rhythms arise from the integration of high-frequency endogenous components and () to quantify the contribution of each higher frequency component to the phenotype of the rhythm. We monitored the performance of 9 experienced pilots by employing an array of cognitive-based tests conducted in a flight simulator so that, over the 6-day experiment, data were obtained for each 2h interval of the 24h. The activity-rest schedule of the subjects, no matter the exact clock time schedule of sleep and activity, always consisted of 14h activity (when they carried out regular professional duties) and 10h rest, with at least 8h of sleep. The simulated combat scenarios consisted of simple and complex tasks associated with target interception, aircraft maneuvering, and target shooting and downing. The results yielded two indices: the number of prominent periodicities in the time series and the relative magnitude of the amplitude of each relative to the construction of the composite 24h waveform. Three cyclic components (8h, 12h, and 24h) composed the observed 24h performance pattern. The dominant period and acrophase (peak time) of the compound output rhythm were determined by the interplay between the amplitudes of the various individual ultradian components. Task complexity (workload) increases the expression of the ultradian entities in the 24h pattern. We constructed a model composed of the multiple ultradian components; the composite output defined a “time span” (of 2h–4h duration) as opposed to an exact “time point” of high and low performance, endowing elevated functional capability. (Chronobiology International, 18(6), 987–1003, 2001) [ABSTRACT FROM AUTHOR]

The possibility that the 24h rhythm output is the composite expression of ultradian oscillators of varying periodicities was examined by assessing the effect of external continuously or pulsed (20-minute) Gonadotropinreleasing hormone (GnRH) infusions on in vitro luteinizing hormone (LH) release patterns from female mouse pituitaries during 38h study spans. Applying stepwise analyses (spectral, cosine fit, best-fit curve, and peak detection analyses) revealed the waveform shape of LH release output patterns over time is composed of several ultradian oscillations of different periods. The results further substantiated previous observations indicating the pituitary functions as an autonomous clock. The GnRH oscillator functions as a pulse generator and amplitude regulator, but it is not the oscillator that drives the ultradian LH release rhythms. At different stages of the estrus cycle, the effect of GnRH on the expression of ultradian periodicities varies, resulting in the modification of their amplitudes but not their periods. The functional output from the system of ultradian oscillators may superimpose a "circadian or infradian phenotype" on the observed secretion pattern. An "amplitude control" hypothesis is proposed: The temporal pattern of LH release is governed by several oscillators that function in conjunction with one another and are regulated by an amplitude-controlled mechanism. Simulated models show that such a mechanism results in better adaptive response to environmental requirements than does a single circadian oscillator. [ABSTRACT FROM AUTHOR]

As soon as they hatch, gallinaceous chicks follow broody hens. This matriarchal unit presents a temporal organization of activity. The ontogeny of this ultradian rhythm of activity was followed in Japanese quail during their first 3 weeks of life. Under controlled laboratory conditions, 12 groups of four chicks were recorded using an activity monitoring system. They were observed between the ages of 2 and 17 days. Chicks in groups presented an ultradian rhythm of activity, with a period that increased significantly from 14.3 ± 1.4 minutes when chicks were 2 days old to 26.0 ± 1.9 minutes when they were 16 days old. The increase of ultradian periodicity was particularly pronounced during their first and third weeks of life. Finally, the ultradian period was correlated positively with body weight of the chicks. (Chronobiology International, 17(6), 767–776, 2000) [ABSTRACT FROM AUTHOR]