Phototaxis by the Dinoflagellate Gymnodinium splendens Lebour*

A microscope-television system was used to monitor quantitatively the behavior of Gymnodinium splendens Lebour in response to light. The predominant behavioral sequence upon stimulation is (a) an initial 2–5 sec cessation of movement (stop-response) followed by (b) positive phototaxis. The action spectra for each response are identical, having maxima at 450 and 280 nm. Upon measuring the percent response to a range of stimulus intensities, it is apparent that a stop-response is not a behavioral prerequisite for phototaxis. An identical circadian rhythm in photoresponsiveness is observed for phototaxis and for the stop-response with greatest light sensitivity occurring during the first 4 hr of the entrained light period. The implication of phototactic sensitivity and the phototactic circadian rhythm in diurnal vertical migration is discussed.     

LACK OF CALBINDIN-D28K ALTERS RESPONSE OF THE MURINE CIRCADIAN CLOCK TO LIGHT

A strong stimulus adjusting the circadian clock to the prevailing light-dark cycle is light. However, the circadian clock is reset by light only at specific times of the day. The mechanisms mediating such gating of light input to the CNS are not well understood. There is evidence that Ca²⁺ ions play an important role in intracellular signaling mechanisms, including signaling cascades stimulated by light. Therefore, Ca²⁺ is hypothesized to play a role in the light-mediated resetting of the circadian clock. Calbindin-D28k (CB; gene symbol: Calb1) is a Ca²⁺ binding protein implicated in Ca²⁺ homeostasis and sensing. The absence of this protein influences Ca²⁺ buffering capacity of a cell, alters spatio-temporal aspects of intracellular Ca²⁺ signaling, and hence might alter transmission of light information to the circadian clock in neurons of the suprachiasmatic nuclei (SCN). We tested mice lacking a functional Calb1 gene (Calb1^?/?) and found an increased phase-delay response to light applied at circadian time (CT) 14 in these animals. This is accompanied by elevated induction of Per2 gene expression in the SCN. Period length and circadian rhythmicity were comparable between Calb1^?/? and wild-type animals. Our findings indicate an involvement of CB in the signaling pathway that modulates the behavioral and molecular response to light. (Author correspondence: urs.albrecht@unifr.ch)     

FAILURE OF EXTRAOCULAR LIGHT TO FACILITATE CIRCADIAN RHYTHM REENTRAINMENT IN HUMANS

Although extraocular light can entrain the circadian rhythms of invertebrates and nonmammalian vertebrates, almost all studies show that the mammalian circadian system can only be affected by light to the eyes. The exception is a recent study by Campbell and Murphy that reported phase shifts in humans to bright light applied with fiber-optic pads behind the knees (popliteal region). We tested whether this extraocular light stimulus could accelerate the entrainment of circadian rhythms to a shift of the sleep schedule, as occurs in shift work or jet lag. In experiment 1, the sleep/dark episodes were delayed 8h from baseline for 2 days, and 3h light exposures were timed to occur before the temperature minimum to help delay circadian rhythms. There were three groups: (1) bright (about 13,000 lux) extraocular light from fiber-optic pads, (2) control (dim light, 10–20 lux), and (3) medium-intensity (about 1000 lux) ocular light from light boxes. In experiment 2, the sleep/dark episodes were inverted, and extraocular light was applied either before the temperature minimum to help delay circadian rhythms or after the temperature minimum to help advance rhythms. Circadian phase markers were the salivary dim light melatonin onset (DLMO) and the rectal temperature minimum. There was no evidence that the popliteal extraocular light had a phase-shifting effect in either experiment. Possible reasons for phase shifts in the Campbell and Murphy study and not the current study include the many differences between the protocols. In the current study, there was substantial sleep deprivation before the extraocular light was applied. There was a large shift in the sleep/dark schedule, rather than allowing subjects to sleep each day from midnight to noon, as in the Campbell and Murphy study. Also, when extraocular light was applied in the current protocol, subjects did not experience a change from sleeping to awake, a change in posture (from lying in bed to sitting in a chair), or a change in ocular light (from dark to dim light). Further research is necessary to determine the conditions under which extraocular light might produce phase shifts in human circadian rhythms. (Chronobiology International, 17(6), 807–826, 2000).     

Interval-specific event related potentials to omitted stimuli in the electrosensory pathway in elasmobranchs: an elementary form of expectation

Multiunit activity and slow local field potentials show Omitted Stimulus Potentials (OSP) in the electrosensory system in rays (Platyrhinoidis triseriata, Urolophus halleri) after a missing stimulus in a 3 to >20 Hz train of V pulses in the bath, at levels from the primary medullary nucleus to the telencephalon. A precursor can be seen in the afferent nerve. The OSP follows the due-time of the first omitted stimulus with a, usually, constant main peak latency, 30–50 ms in medullary dorsal nucleus, 60–100 ms in midbrain, 120–190 ms in telencephalon — as though the brain has an expectation specific to the interstimulus interval (ISI). The latency, form and components vary between nerve, medulla, mid-brain and forebrain. They include early fast waves, later slow waves and labile induced rhythms. Responsive loci are quite local. Besides ISI, which exerts a strong influence, many factors affect the OSP slightly, including train parameters and intensity, duration and polarity of the single stimulus pulses. Jitter of ISI does not reduce the OSP substantially, if the last interval equals the mean; the mean and the last interval have the main effect on both amplitude and latency.Taken together with our recent findings on visually evoked OSPs, we conclude that OSPs do not require higher brain levels or even the complexities of the retina. They appear in primary sensory nuclei and are then modified at midbrain and telencephalic levels. We propose that the initial processes are partly in the receptors and partly in the first central relay including a rapid increase of some depressing influence contributed by each stimulus. This influence comes to an ISI-specific equilibrium with the excitatory influence; withholding a stimulus and hence its depressing influence causes a rebound excitation with a specific latency.Abbreviations DN dorsal nucleus of medullary lateral line lobe - EEG electroencephalogram - EP evoked potential - ERP event related potential - IR induced rhythm - ISI interstimulus interval - OSP omitted stimulus potential - MLN mesencephalic lateral nucleus - P75 positive peak at 75 ms     

Characterization of circadian function in Djungarian hamsters insensitive to short day photoperiod

Summary Djungarian hamsters (Phodopus sungorus sungorus) depend mainly on day length to cue seasonal adjustments. However, not all individuals respond to short day conditions. A previous study from this laboratory proposed that nonresponsiveness to short day conditions rests with a defect in the circadian organization of these hamsters.In this study we found pronounced differences between responsive and nonresponsive hamsters in the expression of circadian rhythmicity under constant darkness and under constant illumination. While responsive hamsters showed a free-running activity pattern with a period of 23.86+0.04 h and responded to brief light pulses with the expected phase delays and phase advances, nonresponsive hamsters exhibited a period of 24.04+0.05 h and responded to light pulses with phase advances. Furthermore, 9 out of 15 responsive hamsters showed a clear split in the activity pattern within 8 weeks under constant light (80–100 lux), while only 1 of the 7 nonresponsive hamsters exhibited a split activity pattern. As a result of these differences in circadian function, nonresponsive Djungarian hamsters are incapable of proper photoperiod time measurement and photoperiod-induced seasonality.Abbreviations PRC phase response curve - ct circadian time - DD constant dark - LL constant light     

Programming of Mice Circadian Photic Responses by Postnatal Light Environment

Early life programming has important consequences for future health and wellbeing. A key new aspect is the impact of perinatal light on the circadian system. Postnatal light environment will program circadian behavior, together with cell morphology and clock gene function within the suprachiasmatic nucleus (SCN) of the hypothalamus, the principal circadian clock in mammals. Nevertheless, it is still not clear whether the observed changes reflect a processing of an altered photic input from the retina, rather than an imprinting of the intrinsic molecular clock mechanisms. Here, we addressed the issue by systematically probing the mouse circadian system at various levels. Firstly, we used electroretinography, pupillometry and histology protocols to show that gross retinal function and morphology in the adult are largely independent of postnatal light experiences that modulate circadian photosensitivity. Secondly, we used circadian activity protocols to show that only the animal''s behavioral responses to chronic light exposure, but not to constant darkness or the acute responses to a light stimulus depend on postnatal light experience. Thirdly, we used real-time PER2::LUC rhythm recording to show long-term changes in clock gene expression in the SCN, but also heart, lung and spleen. The data showed that perinatal light mainly targets the long-term adaptive responses of the circadian clock to environmental light, rather than the retina or intrinsic clock mechanisms. Finally, we found long-term effects on circadian peripheral clocks, suggesting far-reaching consequences for the animal''s overall physiology.     

Effects of a chronic reduction of short-wavelength light input on melatonin and sleep patterns in humans: Evidence for adaptation

Light is an important environmental stimulus for the entrainment of the circadian clock and for increasing alertness. The intrinsically photosensitive ganglion cells in the retina play an important role in transferring this light information to the circadian system and they are elicited in particular by short-wavelength light. Exposure to short wavelengths is reduced, for instance, in elderly people due to yellowing of the ocular lenses. This reduction may be involved in the disrupted circadian rhythms observed in aged subjects. Here, we tested the effects of reduced blue light exposure in young healthy subjects (n?=?15) by using soft orange contact lenses (SOCL). We showed (as expected) that a reduction in the melatonin suppressing effect of light is observed when subjects wear the SOCL. However, after chronic exposure to reduced (short wavelength) light for two consecutive weeks we observed an increase in sensitivity of the melatonin suppression response. The response normalized as if it took place under a polychromatic light pulse. No differences were found in the dim light melatonin onset or in the amplitude of the melatonin rhythms after chronic reduced blue light exposure. The effects on sleep parameters were limited. Our results demonstrate that the non-visual light system of healthy young subjects is capable of adapting to changes in the spectral composition of environmental light exposure. The present results emphasize the importance of considering not only the short-term effects of changes in environmental light characteristics.     

Circadian and circatidal locomotory rhythms in the intertidal beetle Thalassotrechus barbarae (Horn): Carabidae

Thalassotrechus barbarae (Horn) is a member of the intertidal crevice fauna. It forages and mates at night outside the crevice but only during periods of low water. Exogenous stimuli probably inhibit emergence and activity when conditions are not favourable but the main timing of activity is endogenously controlled. Under a LD 15:9 regime (270 lux, tungsten light) the insects were active only during the dark period. Under constant conditions (15–16 °C, 0.05 lux) the beetles showed a circatidal and circadian rhythm of locomotory activity. The circadian rhythm, which has an estimated period of 23.9 h, is quite stable, persisting for at least 7 days. The circatidal rhythm persists for 3 days suggesting that it is subordinate to the dominant circadian rhythm; it probably modifies the latter by inhibiting activity during periods of nocturnal high tides. A possible Zeitgeber for the circatidal rhythm is water movement which, like the probable stimulus entraining the circadian rhythm (light), is capable of being perceived by the eyes of this insect.     

Circadian rhythm of autophagy and light responses of autophagy and disk-shedding in the rat retina

Summary The rhythm of autophagic degradation (AV) in visual cell inner segments shows circadian characteristics: it persists under constant conditions of continuous darkness (DD) and continuous light (LL) and can be reentrained to phase-shifts of the light-dark (LD) cycle. However, unlike the rhythm of disk-shedding and many other circadian rhythms, the rhythm of AV persists with a distinct peak even after 3 days of LL and is rapidly abolished to almost baseline levels after 1.5 days of DD, confirming our previous observations of a strong light-dependence of AV. Since the rhythms of disk-shedding and AV reveal this inverse pattern in DD and LL, different regulative mechanisms may be involved.Light stimulation with increasing intensities at day-time and night-time evoked AV responses that increased and disk-shedding responses that decreased at higher intensities. Furthermore, both the AV and phagosome response was different according to day-time or night-time stimulation, pointing towards the possibility of a circadian phase of sensitivity to light.Abbreviations AV autophagic degradation, autophagic vacuole, autophay - LD light dark cycle - DD constant darkness - LL constant light - CNS central nervous system - SCN suprachiasmatic nucleus - DA dopamine - ftc footcandle - ANOVA analysis of variance     

An arousing, musically enhanced bird song stimulus mediates circadian rhythm phase advances in dim light

A musically enhanced bird song stimulus presented in the early subjective night phase delays human circadian rhythms. This study determined the phase-shifting effects of the same stimulus in the early subjective day. Eleven subjects (ages 18-63 yr; mean +/- SD: 28.0 +/- 16.6 yr) completed two 4-day laboratory sessions in constant dim light (<20 lux). They received two consecutive presentations of either a 2-h musically enhanced bird song or control stimulus from 0600 to 0800 on the second and third mornings while awake. The 4-day sessions employing either the stimulus or control were counterbalanced. Core body temperature (CBT) was collected throughout the study, and salivary melatonin was obtained every 30 min from 1900 to 2330 on the baseline and poststimulus/postcontrol nights. Dim light melatonin onset and CBT minimum circadian phase before and after stimulus or control presentation was assessed. The musically enhanced bird song stimulus produced significantly larger phase advances of the circadian melatonin (mean +/- SD: 0.87 +/- 0.36 vs. 0.24 +/- 0.22 h) and CBT (1.08 +/- 0.50 vs. 0.43 +/- 0.37 h) rhythms than the control. The stimulus also decreased fatigue and total mood disturbance, suggesting arousing effects. This study shows that a musically enhanced bird song stimulus presented during the early subjective day phase advances circadian rhythms. However, it remains unclear whether the phase shifts are due directly to effects of the stimulus on the clock or are arousal- or dim light-mediated effects. This nonphotic stimulus mediates circadian resynchronization in either the phase advance or delay direction.     

Differences in circadian patterns between rural and urban populations: An epidemiological study in countryside

The physiological pattern of the sleep–wake cycle is influenced by external synchronizing agents such as light and social patterns, creating variations in each individual’s preferred active and sleep periods. Because of the demands of a 24-h working society, it may be imperative for many people to adapt their sleep patterns (physiologically) to their daily activities. Therefore, we analyzed the difference in sleep patterns and chronobiological parameters between an essentially rural farming and urban small-town populations. We studied 5942 subjects (women, 67.1%, N?=?3985; mean age, 44.3?±?13.1 years), from which the chronotype, circadian sleep pattern, and period of light exposure were collected using the Munich Chronotype Questionnaire (MCTQ). A structured questionnaire was also made for collection of social and demographic information. Compared with the urban population (N?=?3427, 57.7%), the rural population (N?=?2515, 42.3%) presented a more predominantly early sleep pattern, as determined by the mid-sleep phase (rural: 2.26?±?1.16; urban: 3.15?±?1.55; t-test, p?<?0.001). We also found less social jetlag (rural: 0.32; urban: 0.55; Mann–Whitney U test, p?<?0.001) and higher light-exposure (rural: 9.55?±?2.31; urban: 8.46?±?2.85; t test, p?<?0.001) in the rural population. Additionally, the rural population presented a higher prevalence of psychiatric disorders (rural: 156, 6.20%; urban: 165, 4.80%; Chi-square, p?<?0.05), and a lower prevalence of metabolic diseases (rural: 143, 5.70%; urban: 225, 6.60%; Chi-square, p?<?0.05). The significant difference in sleep parameters, chronotype, and light exposure between groups remained after multivariate regression analysis (r^2?=?0.41, F?=?297.19, p?<?0.001, β?=?1.208). In this study, there was a significant difference between the rural and urban populations in natural light exposure and sleeping patterns. Because of agricultural work schedules, rural populations spend considerable time outside that is an obligation related to work schedules. Our results emphasize the idea that latitude may not be the main factor influencing individual circadian habits. Rather, circadian physiology adapts to differences in exposure to light (natural and artificial) as well as social and work schedules.     

Circadian clocks in changing weather and seasons: Lessons from the picoalga Ostreococcus tauri

Daylight is the primary cue used by circadian clocks to entrain to the day/night cycle so as to synchronize physiological processes with periodic environmental changes induced by Earth rotation. However, the temporal daylight pattern is not the same every day due to erratic weather fluctuations or regular seasonal changes. Then, how do circadian clocks operate properly in varying weather and seasons? In this paper, we discuss the strategy unveiled by recent studies of the circadian clock of Ostreococcus tauri, the smallest free‐living eukaryotic organism. It combines mechanisms controlling light inputs and clock sensitivity, shaping both the dynamics of the core circadian oscillator and its forcing by light so as to ensure stable and precise synchronization in all weather and seasons. Editor's suggested further reading in BioEssays: Another place, another timer: Marine species and the rhythms of life Abstract     

Seasonal changes in entrainment cues for the circadian rhythm of the supratidal amphipod Talorchestia longicornis

The supratidal amphipod Talorchestia longicornis Say has a circadian rhythm in activity, in which it is active on the substrate surface at night and inactive in burrows during the day. The present study determined: (1) the circadian rhythms in individual versus groups of amphipods; (2) the range of temperature cycles that entrain the circadian rhythm; (3) entrainment by high-temperature cycles versus light?:?dark cycles, and (4) seasonal substrate temperature cycles. The circadian rhythm was determined by monitoring temporal changes in surface activity using a video system. Individual and groups of amphipods have similar circadian rhythms. Entrainment occurred only to temperature cycles that included temperatures below 20°C (10–20, 15–20, 17–19, 15–25°C) but not to temperatures above 20°C (20–25, 20–30°C), and required only a 2°C temperature cycle (17–19°C). Diel substrate temperatures were above 20°C in the summer and below 20°C during the winter. Upon simultaneous exposure to a diel high-temperature cycle (20–30°C) and a light?:?dark cycle phased differently, amphipods entrained to the light?:?dark cycle. Past studies found that a temperature cycle below 20°C overrode the light?:?dark cycle for entrainment. The functional significance of this change in entrainment cues may be that while buried during the winter, the activity rhythm remains in phase with the day?:?night cycle by the substrate temperature cycles. During the summer, T. longicornis switches to the light?:?dark cycle for entrainment, perhaps as a mechanism to phase activity precisely to the short summer nights.     

Energy Stores Are Not Altered by Long-Term Partial Sleep Deprivation in Drosophila melanogaster

Recent human studies reveal a widespread association between short sleep and obesity. Two hypotheses, which are not mutually exclusive, might explain this association. First, genetic factors that reduce endogenous sleep times might also impact energy stores, an assertion that we confirmed in a previous study. Second, metabolism may be altered by chronic partial sleep deprivation. Here we address the second assertion by measuring the impact of long-term partial sleep deprivation on energy stores using Drosophila as a model. We subjected flies to long-term partial sleep deprivation via two different methods: a mechanical stimulus and a light stimulus. We then measured whole-body triglycerides and glycogen, two important sources of energy for the fly, and compared them to un-stimulated controls. We also measured changes in energy stores in response to a random circadian clock shift. Sex and line-dependent alterations in glycogen and/or triglyceride levels occurred in response to the circadian clock shift and in flies subjected to a single night of sleep deprivation using light. Thus, consistent with previous studies, our findings suggest that acute sleep loss and changes to the circadian clock can alter metabolism. Significant changes in energy stores were also observed when flies were subjected to chronic sleep loss via the mechanical stimulus, although not the light stimulus. Interestingly, mechanical stimulation resulted in the same change in energy stores even when it was not associated with sleep deprivation, suggesting that the changes are caused by stress rather than sleep loss. These findings emphasize the importance of taking stress into account when evaluating the relationship between sleep loss and metabolism.     

The pineal clock affects behavioral circadian rhythms but not photoperiodic induction in the Indian weaver bird (Ploceus philippinus)

We investigated whether pineal is part of the circadian clock system which regulates circadian rhythms of activity and photosensitivity in the Indian weaver bird (Ploceus philippinus). Two experiments were performed. The first experiment examined the induction of testicular growth, and androgen-dependent beak pigmentation and luteinizing hormone (LH)-specific plumage coloration in pinealectomised (pinx) and sham-operated (sham) birds exposed to short day (8 h light: 16 h darkness, 8L:16D) and long day (16L:8D) for 9 months in the late breeding and early regressive phase (October), or the late regressive and preparatory phase (January) of the annual testicular cycle. As expected, short days were non-stimulatory, and long days stimulated testicular growth, beak pigmentation and plumage coloration. There was no difference in the response between pinx and sham birds subjected to short or long days in October, but the response was enhanced in pinx birds that were subjected to long day in January. In the second experiment circadian behavioral rhythms were studied (activity pattern in singly housed birds) in weaver birds first exposed at two different phases of the annual testicular cycle to a stimulatory photoperiod (12L:12D in preparatory phase or 13L:11D in early breeding phase) and then released into dim continuous light (LL_dim). All birds showed synchronization to the light period before and after the pinealectomy; there was no difference in the response between pinx and sham birds. When released into LL_dim, sham birds exhibited circadian rhythmicity continuously, whereas pinx birds lost circadian rhythmicity after some cycles. Considered together, these results suggest that circadian clock residing within the pineal gland regulates the circadian rhythm in activity, but not the circadian rhythm involved in photoperiodic induction of the Indian weaver bird.     

Retinal and extraretinal photoreceptors mediate entrainment of the circadian locomotor rhythm in lizards

Summary The circadian locomotor activity rhythms of 7 species of lizards can readily be entrained (synchronized) toLD12: 12 (30–50 lux: 0) fluorescent light cycles after complete surgical removal of both eyes. Removal of the parietal eye and pineal organ does not prevent entrainment of blinded lizards. Appropriate control experiments established that lightper se, and not low amplitude temperature cycles or other obvious environmental variables, was the entraining stimulus for blinded lizards. In some cases, blocking the penetration of light to the brains of blinded lizards caused them to free-run (express their endogenous circadian rhythm) in the presence of a dim green light cycle, to which they had previously entrained, suggesting that the brain is the site of the extraretinal photoreceptor(s) mediating entrainment. The extraretinal photoreceptor(s) is capable of intensity discrimination since changing the intensity of aLD 12: 12 fluorescent light cycle caused a change in the phase-relationship between the entrained activity rhythm and the light cycle in a blinded gekko. The lateral eyes are also involved in mediating entrainment since removal of the lateral eyes of thoseSceloporus olivaceus which previously entrained to a dim green light cycle [LD 12: 12 (0.05 lux: 0)] caused them to free-run. Also, blinding had noticeable effects on the entrained activity patterns of some species of lizards.I thank Michael Menaker, Jeffrey Elliott, Sue Binkley, Joseph Silver, Ed Kluth, George Wyche, Bruee Rouse, Nancy Leshikar, Lili Mostafavi, Janet Alvis, Celeste Cromack, A. L. Mackey and Jean Rogers for their suggestions and technical assistance. Support for this work was provided by NIH grant HD-03803-02 (to M. Menaker); NSP grant GB-8138 (to M. Menaker); NSF traineeship GZ-1336 (to H. Underwood); and MH traineeship 5T01GM00836-09 (to H. Underwood).     

Attenuation of the Petal Movement Rhythm in Kalanchoë with Light Pulses

The circadian petal movement rhythm of Kalanchoë flowers has been studied. The amplitude of the rhythm can be drastically reduced by an appropriate stimulus of a light pulse. It has also been shown that it is possible to stop the rhythm permanently by administering a single light pulse to the flowers. This is interpreted to indicate that the light pulse has sent the circadian rhythm into a stable state of singularity. The conditions which attenuate the rhythm have been investigated both theoretically (on the basis of a previously published model for circadian rhythms) and experimentally. 120 min red light of 230 μW · cm^?2, starting briefly before the second petal closure about 30 h after transfer to constant safe light conditions is optimal in inducing rhythm-damping. Damping requires the same duration when the light is given at the corresponding phase during the third or fourth cycle of the rhythm. However, in the first cycle 240 min red light of 230 μW · cm^?2 is required to get optimal damping of the rhythm. Conditions to achieve damping for other irradiances are investigated. Individual recordings are presented which show the behaviour of the rhythm when perturbed by light stimuli close to its singularity.     

Short-term and circadian rhythms in the behaviour of the vole,Microtus agrestis (L.)

Summary The activity behaviour of the vole, Microtus agrestis, has been recorded in order to investigate the relationship between short-term rhythm and circadian rhythm. A simple device was developed, allowing separate monitoring of the time spent in or outside the nest, wheel-running, eating and drinking. Under natural light conditions during summer, a distinct differentiation between a short term rhythm of eating and drinking during the day-time and a circadian rhythm of wheel-running during the night was observed. The short-term rhythm depends closely on metabolic demands (hunger, thirst, excretion). Control of these demands by an endogenous oscillation could not be substantiated. The circadian rhythm of wheel-running activity is, however, controlled by an endogenous oscillation, synchronized by light conditions. It is subjected to seasonal variations. a) The threshold of light intensity below which wheel-running occurs is lowest during summer (<0.5 lx) and is higher during spring and autum (> 5 lx). b) Wheel-running is controlled by a circadian oscillation during summer only whereas it is an integrated part of the short-term rhythm during spring and autumn (experiments during the winter have not yet been performed). Experiments gave evidence that the properties of the cage can deeply influence the amount and pattern of wheel-running activity. It is concluded that wheel-running reflects a certain level of excitation, which may be caused by different behavioural intentions. The seasonal changes of the control of wheel-running activity are discussed with respect to this assumption. The relevancy of locomotor activity patterns as usually recorded in the laboratory to reveal the physiological and ecological significance of endogenously controlled behavioural patterns is discussed.Supported by the Deutsche Forschungsgemeinschaft     

A compromise phase position for permanent night shift workers: circadian phase after two night shifts with scheduled sleep and light/dark exposure

Night shift work is associated with a myriad of health and safety risks. Phase-shifting the circadian clock such that it is more aligned with night work and day sleep is one way to attenuate these risks. However, workers will not be satisfied with complete adaptation to night work if it leaves them misaligned during days off. Therefore, the goal of this set of studies is to produce a compromise phase position in which individuals working night shifts delay their circadian clocks to a position that is more compatible with nighttime work and daytime sleep yet is not incompatible with late nighttime sleep on days off. This is the first in the set of studies describing the magnitude of circadian phase delays that occurs on progressively later days within a series of night shifts interspersed with days off. The series will be ended on various days in order to take a "snapshot" of circadian phase. In this set of studies, subjects sleep from 23:00 to 7:00 h for three weeks. Following this baseline period, there is a series of night shifts (23:00 to 07:00 h) and days off. Experimental subjects receive five 15 min intermittent bright light pulses (approximately 3500 lux; approximately 1100 microW/cm2) once per hour during the night shifts, wear sunglasses that attenuate all visible wavelengths--especially short wavelengths ("blue-blockers")--while traveling home after the shifts, and sleep in the dark (08:30-15:30 h) after each night shift. Control subjects remain in typical dim room light (<50 lux) throughout the night shift, wear sunglasses that do not attenuate as much light, and sleep whenever they want after the night shifts. Circadian phase is determined from the circadian rhythm of melatonin collected during a dim light phase assessment at the beginning and end of each study. The sleepiest time of day, approximated by the body temperature minimum (Tmin), is estimated by adding 7 h to the dim light melatonin onset. In this first study, circadian phase was measured after two night shifts and day sleep periods. The Tmin of the experimental subjects (n=11) was 04:24+/-0.8 h (mean+/-SD) at baseline and 7:36+/-1.4 h after the night shifts. Thus, after two night shifts, the Tmin had not yet delayed into the daytime sleep period, which began at 08:30 h. The Tmin of the control subjects (n=12) was 04:00+/-1.2 h at baseline and drifted to 4:36+/-1.4 h after the night shifts. Thus, two night shifts with a practical pattern of intermittent bright light, the wearing of sunglasses on the way home from night shifts, and a regular sleep period early in the daytime, phase delayed the circadian clock toward the desired compromise phase position for permanent night shift workers. Additional night shifts with bright light pulses and daytime sleep in the dark are expected to displace the sleepiest time of day into the daytime sleep period, improving both nighttime alertness and daytime sleep but not precluding adequate sleep on days off.