Responsiveness to light of the circadian clock controlling eclosion in the blowfly, Lucilia cuprina

ABSTRACT. Eclosion in Lucilia cuprina (Wiedemann) occurs near dawn. The rhythm of eclosion persists in both darkness and constant light of high intensity (490μW cm^-2) with a period close to 24h. The sensitivity to light of the circadian clock controlling eclosion varies greatly according to the stage of the life cycle. During larval life the free running rhythm in darkness can be phase shifted by light pulses of 100μW cm^-2 intensity, with the transition from a Type 1 phase response curve to a Type 0, occurring with pulses of between 1 and 8h. Extending the last light period of LD to 24 h followed by constant darkness resets the phase of the rhythm by 12h, a transition from constant light to constant darkness initiates rhythmicity in flies made arrhythmic by being reared from eggs collected from adults maintained in constant light. After pupariation, the rhythm is relatively insensitive to light. Rhythmicity is sometimes induced by a transition from constant light to constant darkness, but the phase of the rhythm is not shifted by extending the last light period of LD before entering constant darkness. Repeated LD cycles applied after pupariation initiate and entrain the rhythm.     

Photic entrainment of circadian activity patterns in the tropical labrid fish Halichoeres chrysus

Yellow wrasses (Halichoeres chrysus) show clear daily activity patterns. The fish hide in the substrate at (subjective) night, during the distinct rest phase. Initial entrainment in a 12h:12h light-dark (12:12 LD) cycle (mean period 24.02h, SD 0.27h, n = 16 was followed by a free run (mean period 24.42h, SD 1.33h) after transition into constant dim light conditions. Light pulses of a comparable intensity as used in the light part of the LD cycles did not result in significant phase shifts of the free-running rhythm in constant darkness. Application of much brighter 3h light pulses resulted in a phase-response curve (PRC) for a fish species, with pronounced phase advances during late subjective night. The PRCs differed from those mainly obtained in other vertebrate taxa by the absence of significant phase delays in the early subjective night. At that circadian phase, significant tonic effects of the light pulses caused a shortening of the circadian period length. Entrainment to skeleton photoperiods of 1:11 LD was observed in five of six wrasses exposed, also after a 3h phase advance of this LD cycle. Subsequently, a 1:11.25 LD cycle resulted in entrainment in four of the six fish. It is suggested that the expression of the circadian system in fish can be interpreted as a functional response to a weak natural zeitgeber, as present in the marine environment. This response allows photic entrainment as described here in the yellow wrasse. (Chronobiology International, 17(5), 613-622, 2000)     

PHOTIC ENTRAINMENT OF CIRCADIAN ACTIVITY PATTERNS IN THE TROPICAL LABRID FISH HALICHOERES CHRYSUS

Yellow wrasses (Halichoeres chrysus) show clear daily activity patterns. The fish hide in the substrate at (subjective) night, during the distinct rest phase. Initial entrainment in a 12h:12h light-dark (12:12 LD) cycle (mean period 24.02h, SD 0.27h, n = 16 was followed by a free run (mean period 24.42h, SD 1.33h) after transition into constant dim light conditions. Light pulses of a comparable intensity as used in the light part of the LD cycles did not result in significant phase shifts of the free-running rhythm in constant darkness. Application of much brighter 3h light pulses resulted in a phase-response curve (PRC) for a fish species, with pronounced phase advances during late subjective night. The PRCs differed from those mainly obtained in other vertebrate taxa by the absence of significant phase delays in the early subjective night. At that circadian phase, significant tonic effects of the light pulses caused a shortening of the circadian period length. Entrainment to skeleton photoperiods of 1:11 LD was observed in five of six wrasses exposed, also after a 3h phase advance of this LD cycle. Subsequently, a 1:11.25 LD cycle resulted in entrainment in four of the six fish. It is suggested that the expression of the circadian system in fish can be interpreted as a functional response to a weak natural zeitgeber, as present in the marine environment. This response allows photic entrainment as described here in the yellow wrasse. (Chronobiology International, 17(5), 613–622, 2000)     

Effect of light on the development of the circadian rhythm of motor activity in the mouse

In previous experiments, we found that rats raised in constant light (LL) manifested a more robust circadian rhythm of motor activity in LL and showed longer phase shifts after a light pulse in constant darkness (DD) than those raised under constant darkness. In addition, we observed that the effects produced by constant light differed depending on the time of postnatal development in which it was given. These results suggest that both sensitivity to light and the functioning of the circadian pacemaker of the rat could be affected by the environmental conditions experienced during postembryonic development. Thus, the present experiment aimed to study whether postnatal exposure to light could also affect the circadian system of the mouse. Three groups of mice were formed: One group was raised under constant darkness during lactation (DD group), the second under constant light (LL group), and the third under light-dark cycles (LD group). After lactation, the three groups were submitted first to constant light of high intensity, then to LD cycles, and finally to constant darkness. In the DD stage, a light pulse was given. Finally, mice were submitted to constant light of low intensity. We observed that the circadian rhythm of the DD group was more disturbed under constant light than the rhythm of the LL group, and that, when light intensity increased, the period of the rhythm of the DD group lengthened more than that of the LL group. No significant differences among the groups were found in the phase shift induced by the light pulse. Therefore, it appears that DD mice are more sensitive to light than their LL counterparts. However, at present there is no evidence to affirm that the light environment experienced by the mouse during postnatal development affects the circadian pacemaker. (Chronobiology International, 18(4), 683-696, 2001)     

EFFECT OF LIGHT ON THE DEVELOPMENT OF THE CIRCADIAN RHYTHM OF MOTOR ACTIVITY IN THE MOUSE

In previous experiments, we found that rats raised in constant light (LL) manifested a more robust circadian rhythm of motor activity in LL and showed longer phase shifts after a light pulse in constant darkness (DD) than those raised under constant darkness. In addition, we observed that the effects produced by constant light differed depending on the time of postnatal development in which it was given. These results suggest that both sensitivity to light and the functioning of the circadian pacemaker of the rat could be affected by the environmental conditions experienced during postembryonic development. Thus, the present experiment aimed to study whether postnatal exposure to light could also affect the circadian system of the mouse. Three groups of mice were formed: One group was raised under constant darkness during lactation (DD group), the second under constant light (LL group), and the third under light-dark cycles (LD group). After lactation, the three groups were submitted first to constant light of high intensity, then to LD cycles, and finally to constant darkness. In the DD stage, a light pulse was given. Finally, mice were submitted to constant light of low intensity. We observed that the circadian rhythm of the DD group was more disturbed under constant light than the rhythm of the LL group, and that, when light intensity increased, the period of the rhythm of the DD group lengthened more than that of the LL group. No significant differences among the groups were found in the phase shift induced by the light pulse. Therefore, it appears that DD mice are more sensitive to light than their LL counterparts. However, at present there is no evidence to affirm that the light environment experienced by the mouse during postnatal development affects the circadian pacemaker. (Chronobiology International, 18(4), 683–696, 2001)     

The effects of pinealectomy and blinding on the circadian locomotor activity rhythm in the Japanese newt,Cynops pyrrhogaster

We examined the effects of pinealectomy and blinding (bilateral ocular enucleation) on the circadian locomotor activity rhythm in the Japanese newt, Cynops pyrrhogaster. The pinealectomized newts were entrained to a light-dark cycle of 12 h light and 12 h darkness. After transfer to constant darkness they showed residual rhythmicity for at least several days which was gradually disrupted in prolonged constant darkness. Blinded newts were also entrained to a 12 h light/12 h dark cycle. In subsequent constant darkness they showed free-running rhythms of locomotor activity. However, the freerunning periods noticeably increased compared with those observed in the previous period of constant darkness before blinding. In blinded newts entrained to the light/dark cycle the activity rhythms were gradually disrupted after pinealectomy even in the presence of the light/dark cycle. These results suggest that both the pineal and the eyes are involved in the newt's circadian system, and also suggest that the pineal of the newt acts as an extraretinal photoreceptor which mediates the entrainment of the locomotor activity rhythm.Abbreviations circadian period - DD constant darkness - LD cycle, light-dark cycle - LD 12:12 light-dark cycle of 12 h light and 12 h darkness     

Psi-Mutation Affects Phase Angle Difference, Free-Running Period and Phase Shifts in Aedes krombeini (Stegomyia)

A new mutation, designated as psi-mutant, affecting the timing of the circadian oviposition rhythm was discovered the in natural population of Aedes krombeini . This mutation advanced the phase of the oviposition median in an entraining light-dark cycle of 12:12 h by ca. 7.0 h and shortened the free running period t in constant darkness (DD) by ca. 4.0 h. Early oviposition in psi-mutants was also observed when while free-running in DD they were subjected to 24-h temperature cycles (29°C for 12 h and l8°C for l2 h). When the phase response curves (PRCs) for light pulses against DD as background were measured, the PRC for the psi-mutant had large delaying phase shifts, whereas, that of the wild strain had small delaying phase shifts.     

Psi-Mutation Affects Phase Angle Difference,Free-Running Period and Phase Shifts in Aedes krombeini (Stegomyia)

A new mutation, designated as psi-mutant, affecting the timing of the circadian oviposition rhythm was discovered the in natural population of Aedes krombeini. This mutation advanced the phase of the oviposition median in an entraining light-dark cycle of 12:12 h by ca. 7.0 h and shortened the free running period t in constant darkness (DD) by ca. 4.0 h. Early oviposition in psi-mutants was also observed when while free-running in DD they were subjected to 24-h temperature cycles (29°C for 12 h and l8°C for l2 h). When the phase response curves (PRCs) for light pulses against DD as background were measured, the PRC for the psi-mutant had large delaying phase shifts, whereas, that of the wild strain had small delaying phase shifts.     

Circadian rhythm of locomotor activity in the Japanese honeybee, Apis cerana japonica

Abstract.  To reveal circadian characteristics and entrainment mechanisms in the Japanese honeybee Apis cerana japonica , the locomotor-activity rhythm of foragers is investigated under programmed light and temperature conditions. After entrainment to an LD 12 : 12 h photoperiodic regime, free-running rhythms are released in constant dark (DD) or light (LL) conditions with different free-running periods. Under the LD 12 : 12 h regime, activity offset occurs approximately 0.4 h after lights-off transition, assigned to circadian time (Ct) 12.4 h. The phase of activity onset, peak and offset, and activity duration depends on the photoperiodic regimes. The circadian rhythm can be entrained to a 24-h period by exposure to submultiple cycles of LD 6 : 6 h, as if the locomotive rhythm is entrained to LD 18 : 6 h. Phase shifts of delay and advance are observed when perturbing single light pulses are presented during free-running under DD conditions. Temperature compensation of the free-running period is demonstrated under DD and LL conditions. Steady-state entrainment of the locomotor rhythm is achieved with square-wave temperature cycles of 10 °C amplitude, but a 5 °C amplitude fails to entrain.     

The influence of light cycle and circadian rhythm on oviposition in five pyralid moth pests of stored products

ABSTRACT. When batches of about 100 moths of mixed age and sex were kept at 25°C, 65±5%r.h., few eggs were laid by Ephestia cautella, E.kuehniella, E.elutella and Corcyra cephalonica while they were exposed to light of 400-1000lx for up to 12h. Large numbers were laid soon after the light was switched off, however, and the yield during the first hour of darkness increased as the period previously spent in light increased from 1 to 18h. Plodia interpunctella , on the other hand, laid many eggs in light and the numbers laid subsequently during the first hour of darkness in the Slough stock were not influenced by the duration of the light exposure. In LD 12:12, the first four species laid most of their eggs during the scotophase, with E.cautella laying the largest number and E.elutella the smallest. E.cautella transferred from LD 12:12 to constant darkness showed a free-running circadian rhythm for at least three cycles, with most eggs laid near the time that was previously the first hour of darkness, but those transferred to constant light free-ran for only one cycle.     

Large phase-shifts of circadian rhythms caused by induced running in a re-entrainment paradigm: The role of pulse duration and light

Summary Bouts of induced wheel-running, 3 h long, accelerate the rate of re-entrainment of hamsters' activity rhythms to light-dark (LD) cycles that have been phase-advanced by 8 h (Mrosovsky and Salmon 1987). The bouts of running are given early in the first night of the new LD cycle, and by the second night the phase advance in activity onset already averages 7 h. Such large shifts contrast with the mean phase advance of <1 h at the peak of the phase response curve when hamsters in constant darkness (DD) experience 2-h pulses of induced activity (Reebs and Mrosovsky 1989). The present paper investigates pulse duration and light as possible causes for the discrepancy in shift amplitude between these two studies. In a first experiment, pulses of induced wheel-running 1 h, 3 h, or 5 h long were given at circadian times (CT) 6 and 22-2 to hamsters free-running in DD. Pulses given at CT 6 caused phase-advances of up to 2.8 h, whereas pulses at CT 22-2 resulted in delays of up to 1.0 h. Shifts after 3-h and 5-h pulses did not differ, but were larger than after 1-h pulses, and larger than after the 2-h pulses given in DD by Reebs and Mrosovsky (1989). Thus 3 h appears to be the minimum pulse duration necessary to obtain maximum phase-shifting effects. In a second experiment, the re-entrainment design of Mrosovsky and Salmon (1987) was repeated with the light portion of the shifted LD cycle eliminated. Hamsters exercised for 3 h phase-advanced 2.9 h on average (excluding 2 animals who ran poorly). When the same hamsters were exposed 7 days later to a 14-h light pulse starting 5 h after their activity onset, they advanced by an average of 3.3 h. Adding the average values for activity-induced shifts and light-induced shifts gives a total of about 6 h. Possible synergism between the effects of induced activity and those of light may account for the remaining small difference between this total and the 7-h advances previously reported.Abbreviations CT circadian time - DD constant darkness - LD light-dark - PRC phase response curve - free-running period of rhythm     

Social stimuli fail to act as entraining agents of circadian rhythms in the golden hamster

Summary The ability of social stimuli to act as entraining agents of circadian rhythms was investigated in golden hamsters (Mesocricetus auratus). In a first experiment, pairs of male hamsters (one of them enucleated and the other intact) were maintained under a light-dark (LD) cycle with a period of 23.3 h. Running-wheel activity was recorded to determine the effect of social interaction on the free-running circadian rhythm of activity. In several pairs, general activity and body temperature were also recorded. In all pairs the intact animals entrained to the LD cycle, whereas the activity rhythms of the enucleated animals free-ran with periods of approximately 24 h and showed no apparent sign of synchronization or relative coordination with the other member of the pair. In a second experiment, male hamsters maintained in constant darkness received pulses of social interaction, which have been reported to induce phase shifts of the activity rhythm. Consistent phase shifts in the running-wheel activity rhythm were not induced by the social pulses in our experiment. These results suggest strongly that social stimuli are not effective entraining agents of circadian rhythms in the golden hamster.Abbreviations CT circadian time - LD light-dark     

The semidian rhythm in flowering response of Pharbitis nil in relation to dark period time measurement and to a circadian rhythm

When seedlings of Pharbitis nil Choisy, cv. Violet, are exposed to a single inductive dark period at 27°C, brief interruptions with red light (R) can be promotive after 2–3 h of darkness but increasingly inhibitory to flowering up to the 8–9th h of darkness. This rhythmic response to R interruptions can be advanced in phase by > 1 h when the preceding light period is interrupted with far-red (FR) 2 h before darkness (FR -2 h) or with FR – 15 h, whereas FR –8 h or FR–22 h retard the rhythm. These shifts in the R interruption rhythm are paralleled by equal shifts in the length of the dark period required for flowering. Brief FR interruptions of darkness displayed a similar rhythm which was also advanced by FR –2 h and retarded by FR –8 h. We conclude therefore that the semidian rhythm in the light, which we have previously described, continues through at least the first 12 h of darkness, is manifested in the R interruption rhythm, and determines the critical night length. A circadian rhythm with a marked effect on flowering was also identified, but several lines of evidence suggest that the circadian and semidian rhythms have independent additive effects on flowering and do not appear to show phase interaction.     

Presence of circadian rhythms in the locomotor activity of a cave-dwelling millipede Glyphiulus cavernicolus sulu (Cambalidae, Spirostreptida)

The locomotor activity of the millipede Glyphiulus cavernicolus (Spirostreptida), which occupies the deeper recesses of a cave, was monitored in light-dark (LD) cycles (12h light and 12h darkness), constant darkness (DD), and constant light (LL) conditions. These millipedes live inside the cave and are apparently never exposed to any periodic factors of the environment such as light-dark, temperature, and humidity cycles. The activity of a considerable fraction of these millipedes was found to show circadian rhythm, which entrained to a 12:12 LD cycle with maximum activity during the dark phase of the LD cycle. Under constant darkness (DD), 56.5% of the millipedes (n = 23) showed circadian rhythms, with average free-running period of 25.7h ± 3.3h (mean ± SD, range 22.3h to 35.0h). The remaining 43.5% of the millipedes, however, did not show any clear-cut rhythm. Under DD conditions following an exposure to LD cycles, 66.7% (n = 9) showed faint circadian rhythm, with average free-running period of 24.0h ± 0.8h (mean ± SD, range 22.9h to 25.2h). Under constant light (LL) conditions, only 2 millipedes of 11 showed free-running rhythms, with average period length of 33.3h ± 1.3h. The results suggest that these cave-dwelling millipedes still possess the capacity to measure time and respond to light and dark situations. (Chronobiology International, 17(6), 757-765, 2000)     

Characteristics of a circadian pacemaker in the suprachiasmatic nucleus

Summary The nature of the circadian rhythms of the SCN in a hypothalamic island was examined in male rats by recording multiple unit activity from the SCN for longer durations. Successful continuous recording lasted up to 35 days. Neural activity of the SCN inside the island showed free-running rhythms whose periods were slightly longer than 24 h (Figs. 2, 3, Table 1). When the retino-hypothalamic pathway was spared, re-entrainment to a displaced light and dark cycle was attained following a transition period of a few days (Fig. 4). Phases of the rhythms shifted in a phase-dependent manner in response to single light pulses interrupting constant darkness (Fig. 5 and Fig. 6). These results suggest an endogenous nature of the circadian rhythm of the SCN within the hypothalamic island. Thus, neurons or neuronal networks in the SCN may have not only an inherent ability to generate a circadian rhythm, but also an intricate machinery to regulate its phase. Simultaneous recordings from the left and right SCN showed a slight but visible discrepancy in their phases between the two rhythms in 3 out of 12 cases (Fig. 7).Abbreviations LL constant light - LD light-dark - DD constant darkness - SCN Suprachiasmatic nucleus     

Circadian organization and photoreception in an Australian dasyurid marsupial (Sminthopsis macroura)

Much is known about the formal properties of circadian rhythm regulation and the physiological substrates underlying rhythmicity in nocturnal rodents, but relatively few studies have addressed circadian rhythm regulation in other mammalian taxonomic groups. In this study, some formal and functional aspects of circadian organization in a nocturnal dasyurid marsupial, the stripe-faced dunnart (Sminthopsis macroura), were analyzed. To determine phasic responses to discrete pulses of light, dunnarts were placed in constant darkness (DD) and were periodically administered pulses of bright light at different times of the animals' circadian day. Analysis of phase shifts in response to light indicated a phase response curve that was similar to responses observed in nocturnal rodents. To determine the possibility of extraretinal photoreception mediating photic entrainment, dunnarts were anesthetized and orbitally enucleated while maintained in a light-dark regimen (LD 14:10). All blinded dunnarts free-ran with periods (tau) that were similar to those observed in DD, indicating that entrainment is mediated through ocular photoreception. However, the data also indicated a decrease in activity in blind dunnarts during the last 3-5 hr of the dark phase, raising the possibility of some retention of photoreceptive capacities.     

Circadian rhythm resetting in sparrows: early response to doublet light pulses

Circadian responses were studied using the perching activity of house sparrows (Passer domesticus). The sparrows were subjected to single or double 4-hr light pulses (the single pulses or the second pulses of the doublets scanned 24 hr) in the first cycle after previous entrainment to a light-dark cycle (LD 12:12). The differences in times at which the birds commenced perch-hopping in LD 12:12 before the pulses and in the five cycles immediately following the pulses were determined (phase shifts). A 24-hr time profile for phase shifts in response to single light pulses replicated our previous study: Early-night pulses delayed the rhythm (-1.7 hr), while late-night pulses advanced the rhythm (+3.8 hr). After pretreatment with a light pulse that advanced the birds +2.7 hr, the resetting curve was advanced. There were no delays; the range of average shifts was +0.1 hr to +6.2 hr. After pretreatment with a light pulse that delayed the birds -1.7 hr, the resetting curve was delayed. Average delays as much as -1.1 hr and advances up to +2.1 hr were measured. The data for double pulses were interpreted from predictions made from single-pulse data.     

Photic phase response curve in Octodon degus: assessment as a function of activity phase preference

Light exposure during the early and late subjective night generally phase delays and advances circadian rhythms, respectively. However, this generality was recently questioned in a photic entrainment study in Octodon degus. Because degus can invert their activity phase preference from diurnal to nocturnal as a function of activity level, assessment of phase preference is critical for computations of phase reference [circadian time (CT) 0] toward the development of a photic phase response curve. After determining activity phase preference in a 24-h light-dark cycle (LD 12:12), degus were released in constant darkness. In this study, diurnal (n = 5) and nocturnal (n = 7) degus were randomly subjected to 1-h light pulses (30-35 lx) at many circadian phases (CT 1-6: n = 7; CT 7-12: n = 8; CT 13-18: n = 8; and CT 19-24: n = 7). The circadian phase of body temperature (Tb) onset was defined as CT 12 in nocturnal animals. In diurnal animals, CT 0 was determined as Tb onset + 1 h. Light phase delayed and advanced circadian rhythms when delivered during the early (CT 13-16) and late (CT 20-23) subjective night, respectively. No significant phase shifts were observed during the middle of the subjective day (CT 3-10). Thus, regardless of activity phase preference, photic entrainment of the circadian pacemaker in Octodon degus is similar to most other diurnal and nocturnal species, suggesting that entrainment mechanisms do not determine overt diurnal and nocturnal behavior.     

The two-oscillator circadian system of tree shrews (Tupaia belangeri) and its response to light and dark pulses

The wheel-running activity rhythm of tree shrews (tupaias; Tupaia belangeri) housed in constant darkness (DD) phase-advanced following a 3-hr light pulse at circadian time (CT) 21. Dark pulses of 3 hr presented to tupaias in bright constant light (LL) did not induce significant phase shifts of the free-running activity rhythm, irrespective of the CT. In dim LL, tupaias showed simultaneous splitting of their circadian rhythm of wheel-running activity, nest-box activity, and feeding behavior. Light pulses of 6 hr and 2300 lux were presented to 13 tupaias with split wheel-running activity rhythms. These light pulses induced immediate phase shifts in the two components of the split rhythm in opposite directions. No differences were observed between the light-pulse phase response curves of the two components. Equally large immediate phase advances were induced in both components by light pulses of 230 lux, but not by 23 lux. The final phase shifts were small at all CTs. In two tupaias, activity rhythms transiently split and re-fused. Analysis of the relative position of the components in one of these indicates asymmetry in the coupling between the components.     

PRESENCE OF CIRCADIAN RHYTHMS IN THE LOCOMOTOR ACTIVITY OF A CAVE-DWELLING MILLIPEDE GLYPHIULUS CAVERNICOLUS SULU (CAMBALIDAE,SPIROSTREPTIDA)

The locomotor activity of the millipede Glyphiulus cavernicolus (Spirostreptida), which occupies the deeper recesses of a cave, was monitored in light-dark (LD) cycles (12h light and 12h darkness), constant darkness (DD), and constant light (LL) conditions. These millipedes live inside the cave and are apparently never exposed to any periodic factors of the environment such as light-dark, temperature, and humidity cycles. The activity of a considerable fraction of these millipedes was found to show circadian rhythm, which entrained to a 12:12 LD cycle with maximum activity during the dark phase of the LD cycle. Under constant darkness (DD), 56.5% of the millipedes (n = 23) showed circadian rhythms, with average free-running period of 25.7h ± 3.3h (mean ± SD, range 22.3h to 35.0h). The remaining 43.5% of the millipedes, however, did not show any clear-cut rhythm. Under DD conditions following an exposure to LD cycles, 66.7% (n = 9) showed faint circadian rhythm, with average free-running period of 24.0h ± 0.8h (mean ± SD, range 22.9h to 25.2h). Under constant light (LL) conditions, only 2 millipedes of 11 showed free-running rhythms, with average period length of 33.3h ± 1.3h. The results suggest that these cave-dwelling millipedes still possess the capacity to measure time and respond to light and dark situations. (Chronobiology International, 17(6), 757–765, 2000)