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S Daan

Publications and source records attributed to S Daan.

At least 19 recordsLinked to original sources
PubMed2006

Phase and period responses of the circadian system of mice (Mus musculus) to light stimuli of different duration.

To understand entrainment of circadian systems to different photoperiods in nature, it is important to know the effects of single light pulses of different durations on the free-running system. The authors studied the phase and period responses of laboratory mice (C57BL6J//OlaHsd) to single light pulses of 7 different durations (1, 3, 4, 6, 9, 12, and 18 h) given once per 11 days in otherwise constant darkness. Light-pulse duration affected both amplitude and shape of the phase response curve. Nine-hour light pulses yielded the maximal amplitude PRC. As in other systems, the circadian period slightly lengthened following delays and shortened following advances. The authors aimed to understand how different parts of the light signal contribute to the eventual phase shift. When PRCs were plotted using the onset, midpoint, and end of the pulse as a phase reference, they corresponded best with each other when using the mid-pulse. Using a simple phase-only model, the authors explored the possibility that light affects oscillator velocity strongly in the 1st hour and at reduced strength in later hours of the pulse due to photoreceptor adaptation. They fitted models based on the 1-h PRC to the data for all light pulses. The best overall correspondence between PRCs was obtained when the effect of light during all hours after the first was reduced by a factor of 0.22 relative to the 1st hour. For the predicted PRCs, the light action centered on average at 38% of the light pulse. This is close to the reference phase yielding best correspondence at 36% of the pulses. The result is thus compatible with an initial major contribution of the onset of the light pulse followed by a reduced effect of light responsible for the differences between PRCs for different duration pulses. The authors suggest that the mid-pulse is a better phase reference than lights-on to plot and compare PRCs of different light-pulse durations.

Acclimatization↗
PubMed2005

Within clutch co-variation of egg mass and sex in the black-headed gull.

Female birds of several species have control over the production of daughters and sons. However, most studies failed to find a relationship between egg size and sex. This is intriguing as adjustment of egg size would constitute a powerful tool for the female to meet different resource demands of the sexes, particularly in size dimorphic species. Our results show that, within clutches of black-headed gulls (Larus ridibundus) the proportion of males was positively associated with egg mass. This applied for all three laying positions, independently of the absolute egg mass. There was a significant relationship between the distribution of the sexes over the laying sequence and the egg mass change. When egg mass decreased over the sequence, first-laid eggs were male biased and last-laid eggs female biased, and vice versa. The potential adaptive value of this allocation strategy is evaluated with regard to male sensitivity to egg quality and competitive differences between the sexes.

Animals↗
PubMed2003

Interval timing in mice does not rely upon the circadian pacemaker.

The suprachiasmatic nucleus (SCN) of the hypothalamus is a precise timekeeper that controls and synchronizes the circadian period of countless physiological and behavioural functions and entrains them to the 24 h light/dark cycle. We examined the possibility that it is also indirectly involved in measurement of a briefer interval by observing the effects of lesions targeted at the SCN, and abolishing circadian rhythmicity, upon interval timing behaviour. Fourteen house mice (Mus musculus) were trained to estimate a 10 s interval using a modified peak procedure, and then underwent electrolytic lesions. Six individuals became behaviourally arrhythmic. Peak interval performance was then assessed in 12:12 light/dark conditions and in constant darkness. No significant change in peak characteristics was observed as a consequence of the lesion for either rhythmic or arrhythmic groups. These results show that the accurate measurement of 10 s requires neither a functioning circadian pacemaker nor entrained behavioural rhythmicity.

Animals↗
PubMed2003

Fecal corticosteroids in a territorial bird selected for different personalities: daily rhythm and the response to social stress.

In this study we tested the hypothesis that in a passerine bird (great tit, Parus major) individuals differing for coping strategies differ in the magnitude of the adrenocortical response to social stress as well. Furthermore, we aimed at characterizing daily rhythms in corticosteroid release before and after social stress. We used 16 males from either of two lines bidirectionally selected for different coping strategies (fast and slow explorers). Social stress was induced by confrontation with an aggressive resident male. Corticosteroid metabolites were analyzed in feces collected at 90-min intervals from 900 to 1630 h on a baseline day, on the day of the social conflict, and on the following day. In both days and in both lines levels varied with time of day in a robust rhythm with a peak in the first sample of the morning and a trough at the end of the light phase. This rhythm correlates with activity (perch hopping). An overall increase in levels relative to baseline day was observed between 30 and 140 min after the challenge. Birds of the less aggressive and more cautious line (slow explorers) showed a trend for a higher response compared to birds of the more aggressive and bolder line (fast explorers), which showed almost no response. On the day after the challenge the birds of the slow line exhibited significantly reduced corticosteroid secretion, probably due to an increased negative feedback. The results provide evidence for a physiological basis of different coping strategies in birds, emerging in response to social stress and with a pattern similar to that in other vertebrates.

Adaptation, Psychological↗
PubMed2003

Foraging behavior and physiological changes in precocial quail chicks in response to low temperatures.

We examined whether low ambient temperatures influence foraging behavior of precocial Japanese quail chicks and alter the balance between investment in growth and thermogenic function. To test this, one group of chicks was exposed to 7 degrees C and one group to 24 degrees C during foraging throughout the developmental stage. Chicks adapted well to the temperatures through a high flexibility in behavior and physiological development. In response to cold, chicks shortened foraging bout lengths two- to sixfold, and increased cycle lengths (i.e. length of a brooding bout plus subsequent foraging bout), resulting in a decrease in total foraging time. Body temperature during foraging was lower in cold-exposed chicks but did not drop below 37.8 degrees C, suggesting that the direct cause to end a foraging bout was not body temperature. The metabolic rate of cold-exposed chicks was reduced by 48% to 60% when switching from foraging to brooding, which may be an important factor in determining foraging behavior of precocial chicks. Mass-specific food intake of the cold-exposed chicks exceeded that of warm chicks by 15%. Cold-exposed chicks doubled foraging efficiency to reach this intake during their reduced foraging time. Metabolic rates initially were similar in both groups, but increased rapidly and were elevated in cold-exposed chicks from 15 days of age onward. Growth rate initially was reduced in cold-exposed chicks, and exceeded growth of warm chicks only after 21 days of age. These results suggest that in response to cold, a shift occurs in the balance between growth rate and thermoregulatory function in favor of thermoregulatory function.

Animals↗
PubMed2002

Body temperature patterns before, during, and after semi-natural hibernation in the European ground squirrel.

Ground squirrels undergo extreme body temperature fluctuations during hibernation. The effect of low body temperatures on the mammalian circadian system is still under debate. Using implanted temperature loggers, we recorded body temperature patterns in European ground squirrels kept in an enclosure under natural conditions. Although hibernation onset was delayed, hibernation end corresponded closely to that measured in a field population. Circadian body temperature fluctuations were not detected during deep torpor, but indications of circadian timing of arousal episodes at higher temperatures were found at the beginning and end of hibernation. One male exhibited synchronised arousals to a relatively constant phase of the day throughout hibernation. All animals first entered torpor in the afternoon. Daily body temperature fluctuations were decreased or distorted during the first days after hibernation. We hypothesise that hibernation may affect the circadian system by either decreasing the expression of the circadian oscillator, or by decreasing the amplitude of the circadian oscillator itself. possibly due to gradual, temperature dependent, internal desynchronisation. The latter mechanism may be beneficial because it might facilitate post-hibernation re-entrainment rates.

Animals↗
PubMed2002

Gradual reappearance of post-hibernation circadian rhythmicity correlates with numbers of vasopressin-containing neurons in the suprachiasmatic nuclei of European ground squirrels.

European ground squirrels (Spermophilus citellus) in outside enclosures show suppressed circadian rhythmicity in body temperature patterns during the first days of euthermia after hibernation. This may reflect either gradual reappearance of circadian rhythmicity following suppressed functioning of the circadian system during hibernation, or it may reflect transient days during re-entrainment of the circadian system which, during hibernation, has drifted out of phase with the environmental light-dark cycle. Here we report that animals kept under continuous dim light conditions also showed absence of circadian rhythmicity in activity and body temperature in the first 5-15 days after hibernation. After post-hibernation arrhythmicity, spontaneous circadian rhythms re-appeared gradually and increased daily body temperature range. Numbers of arginine-vasopressin immunoreactive neurons in the suprachiasmatic nuclei correlated positively with individual circadian rhythmicity and increased gradually over time after hibernation. Furthermore, circadian rhythmicity was enhanced rather than suppressed after exposure to a light-dark cycle but not after a single 1-h light pulse (1,700 lux). The results support the view that the functioning of the circadian system in the European ground squirrel is suppressed during hibernation at low temperatures and that it requires several days of euthermia to resume its summer function.

Animals↗
PubMed2002

Restoration of self-sustained circadian rhythmicity by the mutant clock allele in mice in constant illumination.

Mice mutant for the Clock gene display abnormal circadian behavior characterized by long circadian periods and a tendency to become rapidly arrhythmic in constant darkness (DD). To investigate whether this result is contingent on the absence of light, the authors studied the circadian behavior of homozygous Clock mutant mice under conditions of both constant light and DD. Fourteen of 15 Clock/Clock mice stayed rhythmic in constant light of 70 to 170 lux, where 10 of 15 wild-type mice became arrhythmic. In contrast, only 5 of 15 Clock/ Clock mice and 15 of 15 wild-type mice remained rhythmic after 60 cycles when released in DD (dim red light of < 1.5 lux) after 8 days of entrainment. The restoration of self-sustained rhythmicity by the Clock allele cannot be attributed to reduced sensitivity of the system to light It underscores the fact that self-sustainment is not a secure guide to functional organization.

Alleles↗
PubMed2001

Extraocular light therapy in winter depression: a double-blind placebo-controlled study.

BACKGROUND: It has been hypothesized that the circadian pacemaker is phase delayed in seasonal affective disorder, (SAD) winter type, and that the phase advance resulting from morning ocular light accounts for the efficacy of light therapy. Extraocular light has been reported to produce phase-shifts of the human circadian pacemaker. This allows a double-blind, placebo-controlled study of light therapy in SAD. METHODS: Twenty-nine SAD patients participated. Clinical state was measured on days 1, 8, and 15 of the protocol. From days 4 through 8, 15 patients (4 M, 11 F) received extraocular light by fiberoptic illumination, and 14 (4 M, 10 F) placebo (no light) in the popliteal fossae, from 8 AM to 11 AM. In the evenings of days 3 and 8, the salivary dim light melatonin onset (DLMO) was assessed. Patients completed daily self-ratings on mood, alertness, and sleep. RESULTS: Both conditions showed a progressive improvement of clinical state over time. Between conditions, no significant differences were observed in clinical scores, the self-ratings on mood and alertness, and in timing of the DLMO before and directly after treatment. CONCLUSIONS: The response to extraocular light therapy in SAD patients did not exceed its placebo effect. Extraocular light did not induce a phase shift of the circadian pacemaker.

Adult↗
PubMed2001

Temporal organisation of hibernation in wild-type and tau mutant Syrian hamsters.

The temporal pattern of hibernation was studied in three genotypes of Syrian hamsters with different circadian periodicity to assess a potential circadian control of alternating torpor and euthermy. We recorded the pattern of hibernation by measuring activity in continuous dim light and constant environmental temperature (6 +/- 1 degrees C). In spite of differences in the endogenous circadian period of three genotypes (tau +/+: approximately equals 24 h, tau +/-: approximately equals 22 h, and tau -/-: approximately equals 20 h) torpor bout duration was statistically indistinguishable (tau +/+: 86.9+/-5.3 h; tau +/-: 94.2+/-3.3 h; tau -/-: 88.8+/-6.2 h). The time between two consecutive arousals from torpor showed unimodal distributions not significantly different between genotypes. The first entry into torpor occurred within the active phase of the circadian cycle in all genotypes whereas the first arousal from torpor appeared to be timed randomly with respect to the prior circadian cycle. The amplitude of the activity rhythm was lower after hibernation compared with the amplitude before hibernation. The results suggest that in the Syrian hamster the circadian system does not control periodicity of torpor and arousal onsets in prolonged hibernation at 6 degrees C.

Animals↗
PubMed2001

A social conflict increases EEG slow-wave activity during subsequent sleep.

Electroencephalogram (EEG) slow-wave activity (SWA) during non-rapid eye movement (NREM) sleep is widely viewed as an indicator of sleep debt and sleep intensity. In a previous study, we reported a strong increase in SWA during NREM sleep after a social conflict in rats. To test whether this increase in SWA reflects normal physiological sleep or an unrelated by-product of the stress, we now measured the effect of a conflict in combination with extended sleep deprivation by means of gentle handling. We anticipated that if the social defeat-induced SWA reflects a true sleep debt, the drive for it would persist during the extended wakefulness. Male rats were subjected to a 1-h social conflict followed by 5 h of sleep deprivation by gentle handling or to 6 h gentle handling alone. The manipulations took place during the second half of the dark phase and recovery sleep was recorded during the subsequent light phase. Neither of the two procedures caused a significant change in the total duration of NREM or REM sleep thereafter. Yet, both modes of sleep deprivation induced a strong increase in SWA during NREM sleep. This SWA was significantly higher for 6 h after sleep deprivation consisting of a social conflict followed by gentle handling, as compared to sleep deprivation by handling alone. Thus, the SWA increasing effect of the conflict persisted during the extended wakefulness. The data confirm that social defeat stress accelerates the build up of sleep debt and support the notion that sleep debt and subsequent NREM sleep intensity not only depend on the duration of prior wakefulness but also on what animals experience during that waking.

Animals↗
PubMed2001

Maternal and pup genotype contribution to growth in wild-type and tau mutant Syrian hamsters.

The single gene mutation tau in the Syrian hamster-apart from its effect on the circadian organization of locomotor activity--has a pronounced influence on body weight. In this study we investigate the impact of maternal and pup genotypes at the tau-locus on the growth rate of pups. Homozygous tau mutant hamsters (circadian period of 20 hours) had lower growth rates and adult body weights than wild-type hamsters, whereas heterozygous tau mutants (circadian period of 22 hours) were intermediate. In addition, heterozygous pups from heterozygous dams grew heavier than those from wild-type and homozygous dams. The effect of maternal genotype was further evaluated in a cross-foster design, where wild-type and homozygous mutant pups were fostered at birth to either wild-type or homozygous mutant dams. At all ages, the maternal tau genotype had a negative effect on body weight, whereas the pup tau genotype had a positive effect during the preweaning period and a negative effect afterward.

Animals↗
PubMed2001

Temporal organization of feeding in Syrian hamsters with a genetically altered circadian period.

The variation in spontaneous meal patterning was studied in three genotypes (tau +/+, tau +/- and tau -/-) of the Syrian hamster with an altered circadian period. Feeding activity was monitored continuously in 13 individuals from each genotype in constant dim light conditions. All three genotypes had on average six feeding episodes during the circadian cycle (about 20h in homozygous tau mutants and 22h in heterozygotes compared with 24h in wild-type hamsters). Thus, homozygous tau mutant hamsters had significantly more feeding episodes per 24h than wild types, and heterozygotes were intermediate. The average duration of feeding bouts (FBs) was indistinguishable (around 30 minutes) among the three genotypes, whereas the intermeal (IM) intervals were significantly shorter for homozygote tau mutant hamsters (99 minutes), intermediate for heterozygotes (116 minutes), and the longest for wild-type hamsters (148 minutes). Thus, the meal-to-meal duration was on average 25% shorter in homozygous tau mutants (16% in heterozygous) than in wild-type hamsters. The reduction of the circadian period has a pronounced effect on short-term feeding rhythms and meal frequency in hamsters carrying the tau mutation.

Analysis of Variance↗
PubMed2001

Assembling a clock for all seasons: are there M and E oscillators in the genes?

The hypothesis is advanced that the circadian pacemaker in the mammalian suprachiasmatic nucleus (SCN) is composed at the molecular level of a nonredundant double complex of circadian genes (per1, cry1, and per2, cry2). Each one of these sets would be sufficient for the maintenance of endogenous rhythmicity and thus constitute an oscillator. Each would have slightly different temporal dynamics and light responses. The per1/cry1 oscillator is accelerated by light and decelerated by darkness and thereby tracks dawn when day length changes. The per2 /cry2 oscillator is decelerated by light and accelerated by darkness and thereby tracks dusk. These M (morning) and E (evening) oscillators would give rise to the SCN's neuronal activity in an M and an E component. Suppression of behavioral activity by SCN activity in nocturnal mammals would give rise to adaptive tuning of the endogenous behavioral program to day length. The proposition-which is a specification of Pittendrigh and Daan's E-M oscillator model-yields specific nonintuitive predictions amenable to experimental testing in animals with mutations of circadian genes.

Animals↗
PubMed1999

Melatonin suppression by light in humans is maximal when the nasal part of the retina is illuminated.

This study investigated whether sensitivity of the nocturnal melatonin suppression response to light depends on the area of the retina exposed. The reason to suspect uneven spatial sensitivity distribution stems from animal work that revealed that retinal ganglion cells projecting to the suprachiasmatic nuclei (SCN) are unequally distributed in several species of mammals. Four distinct areas of the retinas of 8 volunteers were selectively exposed to 500 lux between 1:30 a.m. and 3:30 a.m. Saliva samples were taken before, during, and after light exposure in 1-h intervals. A significant difference in sensitivity was found between exposure of the lateral and nasal parts of the retinas, showing that melatonin suppression is maximal on exposure of the nasal part of the retina. The results imply that artificial manipulation of the circadian pacemaker to alleviate jet lag, to improve alertness in shift workers, and possibly to treat patients suffering from seasonal affective disorder should encompass light exposure of the nasal retina.

Adult↗
PubMed1999

Natural entrainment without dawn and dusk: the case of the European ground squirrel (Spermophilus citellus).

Observational data collected in the field and in enclosures show that diurnal, burrow-dwelling European ground squirrels (Spermophilus citellus) never were above ground during twilight at dawn or at dusk. The animals emerged on average 4.02 h (SD = 0.45) after civil twilight at dawn and retreated in their burrows on average 2.87 h (SD = 0.47) before civil twilight at dusk. Daily patterns of light perceived by these burrowing mammals were measured with light-sensitive radio collar transmitters in an enclosure (the Netherlands) and in the field (Hungary). The observational data are corroborated by the telemetry data, which show clear daily patterns of timing of light perception including light perceived from the burrow entrances. The first light was observed by the animals on average 3.54 h (enclosure, SD = 0.45) and 3.60 h (field, SD = 0.31) after civil twilight at dawn, whereas the final observed light was on average 3.04 h (enclosure, SD = 0.64) and 2.02 h (field, SD = 0.72) before civil twilight at dusk. Thus, the animals do not perceive the rapid natural light-dark (LD) transitions that occur at civil twilight. Instead, they generate their own pattern of exposure to light within the natural LD cycle. The classical phase response model for entrainment by light or dark pulses cannot explain how the circadian system of this species remains entrained to the external, natural LD cycle while the major LD transitions are created by its own behavior.

Animals↗