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S Daan

Publications and source records attributed to S Daan.

At least 37 records · Page 2Linked to original sources
PubMed1999

Accuracy of circadian entrainment under fluctuating light conditions: contributions of phase and period responses.

The accuracy with which a circadian pacemaker can entrain to an environmental 24-h zeitgeber signal depends on (a) characteristics of the entraining signal and (b) response characteristics and intrinsic stability of the pacemaker itself. Position of the sun, weather conditions, shades, and behavioral variations (eye closure, burrowing) all modulate the light signal reaching the pacemaker. A simple model of a circadian pacemaker allows researchers to explore the impact of these factors on pacemaker accuracy. Accuracy is operationally defined as the reciprocal value of the day-to-day standard deviation of the clock times at which a reference phase (0) is reached. For the purpose of this exploration, the authors used a model pacemaker characterized solely by its momentary phase and momentary velocity. The average velocity determines the time needed to complete one pacemaker cycle and, therefore, is inversely proportional to pacemaker period. The model pacemaker responds to light by shifting phase and/or changing its velocity. The authors assumed further that phase and velocity show small random fluctuations and that the velocity is subject to aftereffects. Aftereffects were incorporated mathematically in a term allowing period to contract exponentially to a stable steady-state value, with a time constant of 69 d in the absence of light. The simulations demonstrate that a pacemaker reaches highest accuracy when it responds to light by simultaneous phase shifts and changes of its velocity. Phase delays need to coincide with slowing down and advances with speeding up; otherwise, no synchronization to the zeitgeber occurs. At maximal accuracy, the changes in velocity are such that the average period of the pacemaker under entrained conditions equals 24 h. The results suggest that during entrainment, the pacemaker adjusts its period to 24 h, after which daily phase shifts to compensate for differences between the periods of the zeitgeber and the clock are no longer necessary. On average, phase shifts compensate for maladjustments of phase and velocity changes compensate for maladjustments of period.

Animals↗
PubMed1999

Nonphotic entrainment in a diurnal mammal, the European ground squirrel (Spermophilus citellus).

Entrainment by nonphotic, activity-inducing stimuli has been investigated in detail in nocturnal rodents, but little is known about nonphotic entrainment in diurnal animals. Comparative studies would offer the opportunity to distinguish between two possibilities. (1) If nonphotic phase shifts depend on the phase of the activity cycle, the phase response curve (PRC) should be about 180 degrees out of phase in nocturnal and diurnal mammals. (2) If nonphotic phase shifts depend on the phase of the pacemaker, the two PRCs should be in phase. We used the diurnal European ground squirrel (Spermophilus citellus) in a nonphotic entrainment experiment to distinguish between the two possibilities. Ten European ground squirrels were kept under dim red light (<1 lux) and 20 +/- 1 degrees C. During the entrainment phase of the experiment, the animals were confined every 23.5 h (T) to a running wheel for 3 h. The circadian rhythms of 6 squirrels entrained, 2 continued to free run, and 2 possibly entrained but displayed arrhythmicity during the experiment. In a second experiment, a photic pulse was used in a similar protocol. Five out of 9 squirrels entrained, 1 did not entrain, and 3 yielded ambiguous results. During stable entrainment, the phase-advancing nonphotic pulses coincided with the end of the subjective day, while phase-advancing light pulses coincided with the start of the subjective day: mean psi(nonphotic) = 11.4 h; mean psi(photic) = 0.9 h (psi defined as the difference between the onset of activity and the start of the pulse). The data for nonphotic entrainment correspond well with those from similar experiments with nocturnal Syrian hamsters where psi(nonphotic) varied from 8.09 to 11.34 h. This indicates that the circadian phase response to a nonphotic activity-inducing stimulus depends on the phase of the pacemaker rather than on the phase of the activity cycle.

Activity Cycles↗
PubMed1999

Accuracy of human circadian entrainment under natural light conditions: model simulations.

The patterns of light intensity to which humans expose their circadian pacemakers in daily life are very irregular and vary greatly from day to day. The circadian pacemaker can adjust to such irregular exposure patterns by daily phase shifts, such as summarized in a phase response curve. It is demonstrated in this paper on the basis of computer simulations applying actually recorded human light exposure patterns that the pacemaker can substantially improve its accuracy by an additional response to light: For that purpose, it should additionally change its angular velocity (and consequently its period tau) in response to light. Reductions of tau in response to light in the morning and increases of tau in response to light in the evening can lead to an increase in entrained pacemaker accuracy with about 25%. Circadian pacemakers have evolved as accurate internal representations of external time, and investigated diurnal mammals all seem to respond to light by changing the period of their circadian pacemaker (in addition to shifting phase). The authors suggest that also human circadian systems take advantage of this possibility and that their pacemakers respond to light by shifting phase and changing period. As a consequence of this postulated mechanism, the simulations demonstrate that the period of the pacemaker under normally entrained conditions is 24 h. The maximum accuracy corresponds to a day-to-day standard deviation of the time of phase 0 of circa 15 min. This is considerably more accurate than the light signal humans usually perceive.

Adult↗
PubMed1998

Forced dissociation of food- and light- entrainable circadian rhythms of rats in a skeleton photoperiod.

To investigate the control over drinking and feeding behavior by the light-entrainable circadian pacemaker, rats were maintained in a 12 h:12 h skeleton photoperiod for 36 days with both food and water restricted to the subjective day. During the restriction period most of the food and water intake was concentrated during the first 4 h of the subjective day. The subsequent release into ad lib conditions under the skeleton photoperiod or continuous dark showed that this increased ingestion during the subjective day persisted for up to 6-10 days. This may indicate the entrainment of a food-entrainable oscillator, which has hitherto been investigated solely in anticipatory activity. The daily activity rhythm returned to its original phase position. Thus the phase of the overt daily rhythm is eventually only determined by the phase of the light-entrainable oscillator (LEO) but can temporarily be influenced by the restriction of food and water access. This restriction apparently stimulated a food-entrainable oscillator in antiphase with the light-entrainable oscillator but failed to phase shift or entrain the light-entrainable oscillator.

Animals↗
PubMed1998

Dissimilarity of slow-wave activity enhancement by torpor and sleep deprivation in a hibernator.

Sleep regulation processes have been hypothesized to be involved in function and timing of arousal episodes in hibernating ground squirrels. We investigated the importance of sleep regulation during arousal episodes by sleep deprivation experiments. After sleep deprivation of 4, 12, and 24 h, starting 4 h after onset of euthermy, a duration-dependent enhancement of slow-wave activity (SWA) of the cortical electroencephalogram during non-rapid eye movement sleep was found, as expected for normal sleep regulation. When sleep deprivation was applied during the initial phase of the arousal episode, in which effects of prior torpor were present in undisturbed recordings, no subsequent recurrence of SWA was found. In addition, prior torpor induced a reduction in the spectral activity of the sigma frequency range (7-14 Hz), which was not observed after sleep deprivation. The effects of torpor and sleep deprivation on subsequent SWA appear qualitatively different. This indicates that effects of deep torpor on sleep are dissimilar to normal sleep regulation.

Animals↗
PubMed1998

Aggressive and sexual social stimuli do not phase shift the circadian temperature rhythm in rats.

The objective of the present study was to determine whether the rat circadian system is sensitive to social stimuli. Male rats were subjected to a sociosexual interaction with an estrous female or to an aggressive interaction with a dominant male conspecific. The interactions lasted for 1 h and took place in the middle of the circadian resting phase. Control animals were picked up and handled for a few minutes, but were otherwise left undisturbed. Animals were housed under constant dim red light during the whole period of the experiment. To assess the effects of the interactions on free-running circadian rhythmicity, body temperature was measured by means of radio telemetry. neither the sociosexual interaction with a female nor the aggressive interaction with another male induced phase shifts or changes in the free-running period. The rat circadian system does not seem to be sensitive to social stimuli directly. Moreover, the finding that aggressive interactions do not phase shift circadian rhythms indicates that the endogenous pacemaker in rats is not sensitive to stressors.

Aggression↗
PubMed1997

Social stress induces high intensity sleep in rats.

We studied the effect of social stress on sleep electroencephalogram (EEG) in rats. Animals were subjected to a single social defeat by introducing them in the cage of an aggressive male conspecific for 1 h. The animals responded to the social conflict by a sharp increase in EEG slow-wave activity (SWA) during non-rapid eye movement sleep (NREM) afterwards. Since SWA has been identified as an indicator of sleep intensity, the results suggest that acute stressors may accelerate the build up of sleep debt. Sleep intensity may, thus, not only depend on the duration of prior wakefulness but also on the nature of the waking experience. The strong increase in SWA after social defeat indicates that sleep may function to offset the mental loads imposed on the nervous system during wakefulness.

Animals↗
PubMed1997

Ambient temperature during torpor affects NREM sleep EEG during arousal episodes in hibernating European ground squirrels.

Ambient temperature (Ta) systematically affects the frequency of arousal episodes in mammalian hibernation. This variation might hypothetically be attributed to temperature effects on the rate of sleep debt increase in torpor. We studied this rate by recording sleep electroencephalogram (EEG) in arousal episodes induced after 4 days of torpor at different Ta. Spontaneous torpor bout duration (TBD) varied with Ta: TBD was maximal at 5.5 degrees C (10.7 days), and was reduced at lower (-5 degrees C: 5.0 days, 0 degrees C: 9.3 days) and higher Ta (10 degrees C: 8.7 days, 15 degrees C: 5.0 days). Slow wave activity (SWA) during non-rapid-eye-movement (NREM) sleep, an indicator for sleep debt, showed initial high values after torpor at Ta ranging from -5 degrees C to 10 degrees C. When torpid at 15 degrees C, SWA was not increased in the subsequent arousal episode. The data are thus inconsistent with a rate of sleep debt explanation for the temperature dependence of TBD.

Animals↗
PubMed1997

Effect of photoperiod on body mass, and daily energy intake and energy expenditure in young rats.

In this experiment we investigate the effect of photoperiod on locomotor activity, body mass, food intake, growth efficiency (relationship between body mass change and food intake), energy expenditure, and body composition in growing Wistar rats. Two groups of animals were subjected to either a long, LD 18:6 (n = 8) or short photoperiod, LD 6:18 (n = 7), during a period of 190 days after weaning. Activity, body mass, food intake, and energy expenditure were measured during the study, as well as body composition at the end of the experiment. We show that growing rats exposed to short photoperiod (a) have a lower rate of weight gain, (b) have similar energy intakes, (c) have lower growth efficiency, (d) have lower daily energy expenditure and resting metabolic rate, and (e) gain less lean body mass than those exposed to long photoperiods. We suggest that the distribution of energy expenditure and food intake over the total 24-h cycle may be responsible for the differences in body weight gain between the two photoperiods.

Age Factors↗
PubMed1997

Sleep during arousal episodes as a function of prior torpor duration in hibernating European ground squirrels.

EEG's were recorded in hibernating European ground squirrels during euthermic arousal episodes at an ambient temperature of 5.5 degrees C. Spontaneous torpor bouts ranged from 6 to 15 days, body temperature during torpor was 7.5 degrees C. The torpor duration prior to EEG measurements was experimentally manipulated: the animals were induced to arouse by gentle handling after torpor of less then 1 day (n = 3), 1-2 days (n = 6), 3-4 days (n = 9) and 5-12 days (n = 9). The animals slept 71.5% of euthermic time, of which 61.4% NREM and 10.2% REM sleep. NREM percentage was slightly positively and REM percentage negatively correlated with prior torpor duration (TD). Spectral analysis showed changes in EEG activity during the euthermic phase in the slow wave frequency range (1-4 Hz) and in higher frequencies. Prior TD specifically affected the slow waves. Slow wave activity decreased exponentially during the euthermic phase. The initial slow wave activity showed a systematic increase with prior TD, which could be described by an exponentially saturating function, albeit with a relatively small time constant compared with spontaneous torpor duration. It is concluded that sleep during arousal episodes following torpor at an ambient temperature of 5.5 degrees C is affected both in structure and intensity by prior TD. The results are consistent with the proposition that torpor inhibits the restorative function of sleep.

Animals↗
PubMed1997

Stress-induced changes in circadian rhythms of body temperature and activity in rats are not caused by pacemaker changes.

Previous work has shown that social stress in rats (i.e., defeat by an aggressive male conspecific) causes a variety of behavioral and physiological changes including alterations in the daily rhythms of body temperature and activity. To study the role of the circadian pacemaker in these stress-induced changes, three experiments were performed, successively addressing pacemaker period, phase, and sensitivity to light. In all experiments, rats were subjected to social stress by placing them in the home cage of a dominant conspecific for 1 h. This was done on 2 consecutive days, between the second and fifth hours of the activity phase. Experimental animals were attacked by the resident and lost the fight as indicated by submissive behavior. Control animals were placed in an unfamiliar but clean and empty cage for 1 h. In Experiment 1, the effects of social stress on the period of the free-running activity rhythm were studied. Rats were individually housed under constant dim red light. Activity was measured with infrared detectors. Social defeat caused a reduction of activity for a number of days, but the period of the free-running rhythm was not affected. In Experiment 2, the authors studied whether social defeat induced acute phase shifts. Body temperature and activity were measured by means of radiotelemetry with intraperitoneally implanted transmitters. After the social interactions, experimental animals were kept under constant dim red light. Social stress caused a profound reduction in the amplitude of the body temperature and activity rhythm, but no significant phase shifts occurred. In Experiment 3, the authors studied whether social defeat affected the circadian pacemaker's sensitivity to light given that the size of light-induced phase shifts is thought to reflect pacemaker amplitude. Again, body temperature and activity were measured by means of telemetry. After double social defeat, animals were kept under continuous dim red light. One day after the second conflict, animals were subjected to a single 1-h light pulse (300 lux) at circadian time 14. The light pulse induced a phase delay of the body temperature rhythm, but there were no significant differences between the stress and control groups. The data indicate that stress-induced changes in activity and temperature rhythm, as well as behavioral and physiological changes found in earlier experiments, are not caused by changes in the circadian pacemaker. More generally, the data support the notion that overt rhythms are not always a reliable indication of pacemaker function.

Aggression↗
PubMed1997

Metabolic rate changes proportionally to circadian frequency in tau mutant Syrian hamsters.

The tau mutation in Syrian hamsters (Mesocricetus auratus) is phenotypically expressed in a period of the circadian rhythm of about 20 h in homozygotes (SS) and about 22 h in heterozygotes (S+). The authors investigate whether this well-defined model for variation in circadian period exhibits associated changes in energy metabolism. In hamsters of the three genotypes (SS, S+, and wild type [WT]), oxygen consumption measurements were performed at 28 degrees C (thermoneutral), 18 degrees C, and (after acclimatization) 10 degrees C. After correction for body mass, SS tau mutant hamsters had a higher overall metabolic rate (average oxygen consumption per hour over 24 h) and a higher resting metabolic rate (the lowest 30-min oxygen consumption in the subjective day) than did WT hamsters at all ambient temperatures. S+ hamsters were intermediate in both after taking body mass into account. The differences in metabolism among the three genotypes indicate that the increase in metabolic rate was statistically indistinguishable from a proportional increase in circadian frequency. The oxygen consumption totals per circadian cycle (24 h for WT, 22 h for S+, and 20 h for SS mutants) were not statistically different among the genotypes after correcting for body mass. The possible roles of pleiotropic effects, of linkage to genes involved in growth and metabolism, and of early ontogenetic influences are briefly discussed.

Animals↗
PubMed1997

Human time perception in temporal isolation: effects of illumination intensity.

Living in isolation from time cues under relatively high and low light intensities for a total (on average) of 24 days, 18 subjects estimated the passage of time by "producing" short (10 to 120 seconds) and long (1h) intervals throughout the experiments. The 1h productions were independent of light intensity and highly positively correlated with the duration of wake times. The short-interval productions were markedly increased under high light intensity. In a subsample of 6 subjects, the interaction between effects of body temperature and light condition on 10-second production was analyzed. Productions were negatively correlated with body temperature. In both dim and bright light, productions decreased by a factor of 0.7 per degree C. In bright light, production was increased by a factor of 1.2 relative to dim light. This effect was not mediated by body temperature, which itself was on average slightly increased in bright light. Since subjective time is slowed by bright light, objective time seems to pass faster in bright light.

Adult↗
PubMed1996

Sex identification in birds using two CHD genes.

In theory, birds should control the sex ratio of the offspring they produce. In practice, we have very limited evidence to support this idea because of our difficulty in sexing nestling birds. In addition, extinction is facing an increasing number of birds. Our ability to help includes captive breeding which, again, is difficult if male and female adults cannot be recognized. Here we describe the discovery of a W-linked gene in the Great tit (Parus major). It is named CHD-W (chromodomain-helicase-DNA-binding protein W-linked), it is highly conserved and it is W-chromosome linked in a range of bird species. These birds also possess a second, non-W-linked CHD gene (CHD-NW). A single, simple polymerase chain reaction technique based on both genes can be used to identify the sex in a wide variety of birds.

Animals↗
PubMed1996

Changes in Behaviour and Body Weight Following a Single or Double Social Defeat in Rats.

In a series of experiments, the consequences of a single and double social conflict on various behaviours and body weight in rats were studied. Animals were subjected to social defeat by placing them into the territory of an aggressive male conspecific for one hour, either once, or twice at the same time on two consecutive days. To assess the consequences of social defeat, three experiments were performed with independent groups of rats. In the first experiment, an open field test was performed two days after the last conflict. Locomotor activity was strongly reduced after social defeat. There were no differences between the single and double defeat group. To assess the effects of social defeat on subsequent social behaviour, a second experiment was performed in which experimental animals were confronted with an unfamiliar non-aggressive rat two days after a single or double conflict. Social defeat resulted in a reduction of social contact with the unfamiliar conspecific. There was no difference between the single and double conflict group. In the third experiment, the effects of social conflict on food intake, body weight and saccharine preference were measured. Food intake was not affected after a single conflict, but in the double conflict group food intake was decreased for several days. Body weight gain was decreased after both single and double social defeat. The decrease was stronger in the double conflict group. Water intake and saccharine preference were not significantly affected. This study revealed that social defeat in rats causes pronounced changes in various behaviours and body weight. Different aspects of behaviour are differentially affected by defeat with respect to the magnitude and time course of the changes induced. Moreover, different behavioural parameters are differentially sensitive to repetition of the stressor.

Journal Article↗
PubMed1993

Phase control of ultradian feeding rhythms in the common vole (Microtus arvalis): the roles of light and the circadian system.

In their ultradian (2- to 3-hr) feeding rhythm, common voles show intraindividual synchrony from day to day, as well as interindividual synchrony between members of the population, even at remote distances. This study addresses the question of how resetting of the ultradian rhythm, a prerequisite for such synchronization, is achieved. Common voles were subjected to short light-dark cycles (1 hr darkness with light varying between 0.7 and 2.5 hr); to T cycles (long light-dark cycles in the circadian range--16 hr darkness and 3-13 hr light); to light pulses (15 min) during different circadian and ultradian phases; and to addition of D2O to the drinking water (25%). Short light-dark cycles and D2O were also applied to voles without circadian rhythmicity, after lesions of the suprachiasmatic nuclei. In these experiments, four hypotheses on synchronization of ultradian rhythmicity were tested: (I) synchronization by a direct response to light; (II) synchronization via the circadian system with multiple triggers, here called "cogs," each controlling a single ultradian feeding bout; and (III and IV) synchronization via the circadian system with a single "cog," which resets an ultradian oscillator and either (III) originates directly from the circadian pacemaker, or (IV) is mediated via the overt circadian activity rhythm. Short light-dark cycles failed to entrain ultradian rhythms, either in circadian-rhythmic or in non-circadian-rhythmic voles; light pulses did not cause phase shifts; and in extreme T cycles no stable phase relationship with light could be demonstrated. Thus, Hypothesis I was rejected. Changes in the circadian period (tau) were generated as aftereffects of light pulses, by entrainment in various T cycles, and by the addition of D2O to the drinking water. These changes in tau did not lead to parallel, let alone proportional, changes in the ultradian period. This excluded Hypothesis II. Both in T-cycle experiments and in the D2O experiments with circadian-rhythmic voles, the phase of ultradian feeding bouts was locked to the end of circadian activity rather than to the most prominent marker of the pacemaker, the onset of circadian activity. This was not expected under Hypothesis III, but was consistent with entrainment via activity (Hypothesis IV). On the basis of these experiments, we conclude that the most likely mechanism of ultradian entrainment is that of a light-insensitive ultradian oscillator, reset every dawn by the termination of the activity phase controlled by the circadian pacemaker, which is itself entrained by the light-dark cycle. Neither in circadian-rhythmic nor in non-circadian-rhythmic voles was the period of the feeding rhythm lengthened by administration of D2O. This insensitivity to deuterium is exceptional among biological rhythms.

Activity Cycles↗