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Constant Light (constant + light)
Selected AbstractsEffect of the dusk photoperiod change from light to dark on the incubation period of eggs of the spotted rose snapper, Lutjanus guttatus (Steindachner)AQUACULTURE RESEARCH, Issue 4 2008Neil J Duncan Abstract Spotted rose snapper, Lutjanus guttatus (Steindachner), eggs were incubated under different photoperiods to examine the effect of photoperiod on incubation. The eggs from two fish were incubated under five artificial photoperiods: constant dark (D), constant light (L) from 06:00 hours and 6, 10 and 14 h of light from 06:00 hours. The eggs from seven other fish were incubated under a natural photoperiod. Different spawning times (21:00 , 01:00 hours) and different photoperiods combined to give the start of the dusk photoperiod change after 11,23 h of incubation. Constant light or applying the dusk photoperiod change after ,20 h of incubation appeared to extend the hatching period. The mean hatching period for groups of eggs incubated in darkness or that received the dusk photoperiod change after ,19 h of incubation (n=8 different groups) was 2 h 15±10 min, which was significantly lower (P<0.05) than the mean hatching period of 4 h±37 min for groups that did not receive the dusk photoperiod change or that received the dusk photoperiod change after ,20 h of incubation (n=9 groups). However, despite these differences, the majority of the eggs hatched during a 2,3 h period from 17 to 20 h of incubation, and a sigmoid regression (r2=0.9) explained the relationship between percentage hatch and hours of incubation for all photoperiod groups. [source] PER2 controls circadian periods through nuclear localization in the suprachiasmatic nucleusGENES TO CELLS, Issue 11 2007Koyomi Miyazaki Molecular circadian clock regulation engages a negative feedback loop comprising components of the negative limb, PERs and CRYs. In addition to the rhythmic transcriptional regulation of clock genes, controlled subcellular localization might contribute to the molecular mechanism of the mammalian circadian clock. To address this issue, we generated transgenic (TG) mice lines harboring either rat PER2 (rPER2) with a deleted nuclear localizing domain [NLD(,)] or intact PER2. In comparison with wild-type (WT) control, the period of the circadian locomotor rhythm in TG mice over-expressing NLD(,) PER2 was longer, while that in TG mice over-expressing intact PER2 was shorter. The nuclear entry of endogenous PER2, CRY1 and CRY2 was delayed in the suprachiasmatic nucleus (SCN) of NLD(,) PER2 TG mice under constant darkness, whereas that of mouse PER2 (mPER2) is accelerated in the SCN of intact PER2 TG mice. Under constant light, the locomotor activity of NLD(,) PER2 TG mice became arrhythmic, whereas WT animals remained rhythmic. These data indicate that PER2 controls circadian periods through nuclear localization in the SCN. In addition, sleep architecture was also affected in intact PER2 TG mice, suggesting PER2 can modulate a sleep molecular mechanism. [source] Modifications of retinal afferent activity induce changes in astroglial plasticity in the hamster circadian clockGLIA, Issue 2 2001Monique Lavialle Abstract The circadian clock, located in the suprachiasmatic nucleus (SCN) of the hypothalamus in mammals, exhibits astroglial plasticity indicated by GFAP expression over the 24-h period. In this study, we evaluated the role of neuronal retinal input in the observed changes. Modifications of retinal input, either by rearing animals under darkness (DD) or under constant light (LL), or by suppressing afferent input (bilateral enucleation), induced drastic changes in astroglial plasticity. In enucleated animals, a dramatic decrease in GFAP expression was evident in the area of the SCN deprived of retinal projections, whereas persistence of a rhythmic variation was in those areas still exhibiting GFAP expression. By contrast, no changes in astrocytic plasticity were detected in hamsters maintained under LL. These data suggest two fundamental roles for astrocytes within the SCN: (1) to regulate and mediate glutamate released by retinal terminals throughout the neuronal network to facilitate photic signal transmission; (2) to contribute to synchronization between suprachiasmatic neurons. GLIA 34:88,100, 2001. © 2001 Wiley-Liss, Inc. [source] Serotonergic potentiation of dark pulse-induced phase-shifting effects at midday in hamstersJOURNAL OF NEUROCHEMISTRY, Issue 3 2008Jorge Mendoza Abstract In mammals, resetting of the suprachiasmatic clock (SCN) by behavioral activation or serotonin (5-HT) agonists is mimicked by dark pulses, presented during subjective day in constant light (LL). Because behavioral resetting may be mediated in part by 5-HT inputs to the SCN, here we determined whether 5-HT system can modulate dark-induced phase-shifts in Syrian hamsters housed in LL. Two hours of darkness at mid-subjective day (circadian time 6; CT-6) resulted in increased concentrations of 5-HT in the SCN tissue and induction of c-FOS expression in the raphe nuclei. Injections of the 5-HT1A/7 agonist (+)8-OH-DPAT or dark pulses at CT-6 induced phase-advances of the wheel-running activity rhythm and down-regulated the expression of the clock genes Per1-2 and c-FOS in the SCN in a similar way. The combination of both treatments [(+)8-OH-DPAT + dark pulses], however, resulted in larger phase-advances, while associated molecular changes were not significantly modified, except for the gene Dbp, in comparison to (+)8-OH-DPAT or dark pulses alone. Dark resetting was blocked by pre-treatment with a 5-HT7 antagonist, but not with a 5-HT1A antagonist. The additive phase-shifts of two different cues to reset the SCN clock open wide the gateway for non-photic shifting, leading to new strategies in chronotherapy. [source] Environmental Modulation of Alcohol Intake in Hamsters: Effects of Wheel Running and Constant Light ExposureALCOHOLISM, Issue 9 2010Steven B. Hammer Background:, Alcohol abuse leads to marked disruptions of circadian rhythms, and these disturbances in themselves can increase the drive to drink. Circadian clock timing is regulated by light, as well as by nonphotic influences such as food, social interactions, and wheel running. We previously reported that alcohol markedly disrupts photic and nonphotic modes of circadian rhythm regulation in Syrian hamsters. As an extension of this work, we characterize the hedonic interrelationship between wheel running and ethanol (EtOH) intake and the effects of environmental circadian disruption (long-term exposure to constant light [LL]) on the drive to drink. Methods:, First, we tested the effect of wheel running on chronic free-choice consumption of a 20% (v/v) EtOH solution and water. Second, the effect of this alcohol drinking on wheel running in alcohol-naive animals was investigated. Third, we assessed the influence of LL, known to suppress locomotor activity and cause circadian rhythm disruption, on EtOH consumption and wheel-running behavior. Results:, Inhibitory effects of wheel running on EtOH intake and vice versa were observed. Exposure to LL, while not affecting EtOH intake, induced rhythm splitting in 75% of the animals. Notably, the splitting phenotype was associated with lower levels of EtOH consumption and preference prior to, and throughout, the period of LL exposure. Conclusions:, These results are evidence that exercise may offer an efficacious clinical approach to reducing EtOH intake. Also, predisposition for light-induced (or other) forms of circadian disruption may modulate the drive to drink. [source] Persistence of a plasma melatonin rhythm in constant darkness and its inhibition by constant light in the sleepy lizard, Tiliqua rugosaJOURNAL OF PINEAL RESEARCH, Issue 1 2006Bruce T. Firth Abstract:, This study determined whether a blood plasma melatonin rhythm persists in constant photothermal environments in the sleepy lizard, Tiliqua rugosa. It builds upon an earlier investigation which provided equivocal results as to whether an in vivo melatonin rhythm persists in constant dark (DD) and light (LL) and temperature in this species. Using more frequent sampling points and new assay techniques, the present study showed that the melatonin rhythm persisted for at least 6 days at temperatures of 25 and 33°C in constant dark (DD). The melatonin rhythm, however, was largely eliminated in constant light (LL) at 33°C, thereby contradicting some previous findings in other species of reptiles where melatonin levels were apparently insensitive to an unexpected pulse of light at night. These results demonstrate that the sleepy lizard has a persistent, possibly circadian rhythm of melatonin in DD and constant temperature, and that the rhythm is inhibited by LL and constant temperature. Therefore, the sleepy lizard pineal gland may be an independent oscillator capable of driving the melatonin rhythm and be a transducer of the seasonally changing external photothermal environment. [source] Effect of stimulation of endogenous melatonin secretion during constant light exposure on 6-sulphatoxymelatonin rhythmicity in ratsJOURNAL OF PINEAL RESEARCH, Issue 1 2000D.J. Kennaway When light is presented unexpectedly at night to rats, melatonin production and secretion is acutely inhibited and the time of onset of production on the subsequent night is altered. In a series of experiments, we examined the effects of 6,12 hr light (200 lux) at night on melatonin metabolite excretion (6-sulphatoxymelatonin, aMT.6S). During the light exposure, we administered isoproterenol to stimulate endogenous production of melatonin by the pineal gland to determine if replacement of melatonin would block any phase shifting effects of the light. Exposure to 6 hr of light either during the first or second half of the night suppressed aMT.6S excretion during the light treatment and delayed the onset of melatonin secretion by 3.7±0.6 and 2.5±0.6 hr, respectively, compared to a change of 0.5±0.1 hr in animals maintained in darkness. Twelve hours light exposure (i.e. one night of continuous light) suppressed aMT.6S excretion completely and resulted in a delay in the onset the next night of 2.1±0.7 hr. When propranolol (10 mg/kg) was administered at 2-hr intervals during darkness, aMT.6S excretion was suppressed throughout the night, but on the subsequent release into constant darkness the onset of excretion was not delayed (0.6±0.1 hr delay). Administration of isoproterenol (10 mg/kg) to animals in constant light, at the time of expected lights off (CT12), and 5 hr later (CT17) resulted in an increase in melatonin production and aMT.6S excretion that was similar in duration and amount to the control night. The stimulation of endogenous melatonin production failed to block the phase shifting effects of the light exposure and, in fact, appeared to potentiate the delay at least on the first night (4.2±0.9 hr). The timing of the release into constant darkness following the light treatment had an unexpected effect on melatonin production on the cycle after treatment. Thus, animals exposed to 12 hr light and released into darkness at the normal time of lights off as above had a delay of about 2 hr and excreted 71±18% of the aMT.6S excreted on a control night. Animals released into darkness at the expected time of lights on failed to excrete more than 20 pmol/hr (i.e. no onset of excretion could be determined) at any time on the first subjective night after light treatment, which was no different from the excretion during the light treatment. On the next subjective night, the onset was delayed as expected and the amount of aMT.6S produced was restored. Treatment with isoproterenol at CT12 and CT17 failed to affect either the amount of aMT.6S excreted on the first subjective night after light treatment or the phase delay on the second night after treatment. The failure to produce melatonin on the first subjective night after 12 hr light exposure and release into darkness at CTO was not due to failure at the level of the pineal gland since injection of isoproterenol at CT12 and CT17 on the first subjective night after light restored the normal amount of melatonin production. These results suggest that the absence of melatonin during light stimulation at night is not responsible for the phase delay in melatonin production and excretion on subsequent nights. The basis of the failure of the rats to commence melatonin production following 12 hr extended light exposure followed immediately by continuous darkness is not known. [source] The Arabidopsis SPA1 gene is required for circadian clock function and photoperiodic floweringTHE PLANT JOURNAL, Issue 5 2006Masaki Ishikawa Summary Arabidopsis phytochrome A (phyA) regulates not only seed germination and seedling de-etiolation but also circadian rhythms and flowering time in adult plants. The SUPPRESSOR OF PHYA-105 (SPA1) acts as a negative regulator of phyA-mediated de-etiolation of young seedlings, but its roles in adult plants have not yet been described. Here, we show that SPA1 is involved in regulating circadian rhythms and flowering time in plants. Under constant light, the abundance of SPA1 protein exhibited circadian regulation, whereas under constant darkness, SPA1 protein levels remained unchanged. These results indicate that the SPA1 protein is controlled by the circadian clock and light signals. In addition, the spa1-3 mutation slightly shortened the circadian period of CCA1, TOC1/PRR1 and SPA1 transcript accumulation under constant light. Phenotypic analysis showed that the spa1-3 mutant flowers early under short-day (SD) but not long-day (LD) conditions. Consistent with this finding, transcripts encoding flowering locus T (FT), which promotes flowering, increased in spa1-3 under only SD conditions, although the CONSTANS (CO) transcript level was not affected under either SD nor LD conditions. Our results indicate that SPA1 not only negatively controls phyA-mediated signaling in seedlings, but also regulates circadian rhythms and flowering time in plants. [source] RFI2, a RING-domain zinc finger protein, negatively regulates CONSTANS expression and photoperiodic floweringTHE PLANT JOURNAL, Issue 5 2006Mingjie Chen Summary The red and far-red light-absorbing phytochromes interact with the circadian clock, a central oscillator that sustains a 24-h period, to measure accurately seasonal changes in day-length and regulate the expression of several key flowering genes. The interactions and subsequent signalling steps upstream of the flowering genes such as CONSTANS (CO) and FLOWERING LOCUS T (FT) remain largely unknown. We report here that a photomorphogenic mutant, red and far-red insensitive 2-1 ( rfi2-1), flowered early particularly under long days. The rfi2-1 mutation also enhanced the expression of CO and FT under day/night cycles or constant light. Both co-2 and gigantea-2 (gi-2) were epistatic to rfi2-1 in their flowering responses. The gi-2 mutation was also epistatic to the rfi2-1 mutation in the expression of CO and hypocotyl elongation. However, the rfi2-1 mutation did not affect the expression of GI, a gene that mediates between the circadian clock and the expression of CO. Like many other flowering genes, the expression of RFI2 oscillated under day/night cycles and was rhythmic under constant light. The amplitude of the rhythmic expression of RFI2 was significantly reduced in phyB-9 or lhy-20 plants, and was also affected by the gi-2 mutation. As previously reported, the gi-2 mutation affects the period length and amplitude of CCA1 and LHY expression, and GI may act through a feedback loop to maintain a proper circadian function. We propose a regulatory step in which RFI2 represses the expression of CO, whereas GI may maintain the proper expression of RFI2 through its positive action on the circadian clock. The regulatory step serves to tune the circadian outputs that control the expression of CO and photoperiodic flowering. [source] Large-scale screening of Arabidopsis circadian clock mutants by a high-throughput real-time bioluminescence monitoring systemTHE PLANT JOURNAL, Issue 1 2004Kiyoshi Onai Summary Using a high-throughput real-time bioluminescence monitoring system, we screened large numbers of Arabidopsis thaliana mutants for extensively altered circadian rhythms. We constructed reporter genes by fusing a promoter of an Arabidopsis flowering-time gene , either GIGANTEA (GI) or FLOWERING LOCUS T (FT) , to a modified firefly luciferase gene (LUC+), and we transferred the fusion gene (PGI::LUC+ or PFT::LUC+) into the Arabidopsis genome. After mutagenesis with ethyl methanesulfonate, 50 000 M2 seedlings carrying the PGI::LUC+ and 50 000 carrying PFT::LUC+ were screened their bioluminescence rhythms. We isolated six arrhythmic (AR) mutants and 29 other mutants that showed more than 3 h difference in the period length or phase of rhythms compared with the wild-type strains. The shortest period length was 16 h, the longest 27 h. Five of the six AR mutants carrying PGI::LUC+ showed arrhythmia in bioluminescence rhythms in both constant light and constant dark. These five AR mutants also showed arrhythmia in leaf movement rhythms in constant light. Genetic analysis revealed that each of the five AR mutants carried a recessive mutation in a nuclear gene and the mutations belonged to three complementation groups, and at least one of which was mapped on a novel locus. Our results suggest that the three loci identified here may contain central clock or clock-related genes, at least one of which may be a novel. [source] Intraovarian Localization of Growth Factors in Induced Cystic Ovaries in RatsANATOMIA, HISTOLOGIA, EMBRYOLOGIA, Issue 2 2007H. H. Ortega Summary We hypothesized that the special hormonal environment present in animals with cystic ovarian disease (COD) interferes with cellular production of growth factors (GFs). The objective of the present study was to characterize the expression of insulin-like growth factor (IGF)-I, fibroblast growth factor (FGF)-2 and vascular endothelial growth factor (VEGF) in induced COD using immunohistochemistry. We used an experimental model based on the exposure to constant light of adult rats during 15 weeks. We quantified the expression of GFs in cystic and normal ovaries by the Immunohistochemical Stained Area (IHCSA). In animals with COD, a significant reduction in the IHCSA of IGF-I in the follicular fluid, theca and granulosa layers of cysts occurred; and an increase in the interstitial tissue with regard to the control group. We found moderate immunoreactivity of FGF-2 in granulosa and theca layers of secondary and tertiary follicles and lower expression in the granulosa and theca interna layers of cystic follicles. Immunoexpression of VEGF was found in granulosa and theca cells of secondary and tertiary follicles. This study shows changes in the ovarian expression of IGF-I, FGF-2 and VEGF in induced COD. We can propose that an alteration in the control of the follicular dynamic, through the GFs, added to other features, could be involved in the ovarian cyst pathogenesis. [source] Photic and non-photic entrainment on daily rhythm of locomotor activity in goatsANIMAL SCIENCE JOURNAL, Issue 1 2010Claudia GIANNETTO ABSTRACT We studied the photic (L/D cycle) and non-photic (restricted feeding) entrainment on the patterns of daily rhythm of total locomotor activity in goats. Six female Maltese goats were subjected to three different artificial L/D cycles: 12/12 L/D, 12/12 D/L and constant light. During the 12/12 L/D and 12/12 D/L, food and water were available ad libitum. During constant light, animals were subjected to a restricted feeding treatment. Total activity was recorded by means of an actigraphy-based data logger (Actiwatch-Mini®). Our results showed that goats exhibited clear daily rhythms of activity in 12/12 L/D cycle, 12/12 D/L cycle and constant light, although they showed FAA prior the feeding time during the restricted feeding treatment. Goats were diurnal, with activity consistently beginning promptly following the onset of light. Even when the L/D cycle was delayed by 12 h on some days, to the daily rhythm was re-established. During the constant light period, the onset of activity was linked to the time of food administration. Our study evidences two factors for the rhythm of total locomotor activity in goats: light stimuli (photic) and food access (non photic), strongly coupled to permit organisms the adaptive temporal coordination of behaviour with stable and unstable environmental periodicities. [source] Effects of different photoperiods on growth, stress and haematological parameters in juvenile great sturgeon Huso husoAQUACULTURE RESEARCH, Issue 16 2009Ali Bani Abstract The effects of constant light (24L:00D), no light (00L:24D) and two light,dark periods (18L:06D;12L:12D) on the growth, stress and haematological variables were assessed in juvenile great sturgeon, Huso huso. During the 8-week experimental period, juveniles (22.5 ± 0.6 g) were kept under a 150 lx light intensity in fibreglass tanks (0.8 m2, 500 L). Differences in growth were insignificant during the experiment, but lactate levels were higher in the 00L:24D and 24L:00D photoperiods compared with 12L:12D and 18L:06D photoperiods. Cortisol levels did not show differences among the various photoperiods. At the end of the experimental period, fish reared under a 12L:12D photoperiod had higher haemoglobin values and erythrocyte numbers than in the other photoperiods, while no differences were found between groups with regard to haematocrit values or leucocyte numbers. The highest survival rate (89%) was observed in the 12L:12D period in which the levels of lactate and cortisol as stress indicators were minimal. The results indicate that various photoperiods cause different stress levels in juvenile great sturgeon and have no significant effects on growth, at least in short time periods. [source] Timing and duration of constant light affects rainbow trout (Oncorhynchus mykiss) growth during autumn,spring grow-out in freshwaterAQUACULTURE RESEARCH, Issue 13 2009John Taylor Abstract Photoperiod enhancement of growth is becoming an area of increasing interest as a means of enhancing rainbow trout production efficiency in commercial practice. This paper examines the possible implications of shortening periods of constant light (LL) exposure on rainbow trout growth during autumn,spring grow-out under ambient water temperatures in freshwater to portion size. Triplicate groups of juvenile all-female rainbow trout were permanently exposed to LL in October, November, December or January. Growth was monitored and compared with those maintained under a simulated natural photoperiod (SNP) until the following May. Permanent exposure to LL (all treatments) resulted in significantly greater weight gain of rainbow trout than those under SNP. Furthermore, greatest growth was achieved when fish were left permanently exposed to LL from October. These findings suggest there may be implications for fish farmers if the period of photoperiod exposure is reduced, or timing of application is not considered with regards to ambient water temperatures. [source] Effect of the dusk photoperiod change from light to dark on the incubation period of eggs of the spotted rose snapper, Lutjanus guttatus (Steindachner)AQUACULTURE RESEARCH, Issue 4 2008Neil J Duncan Abstract Spotted rose snapper, Lutjanus guttatus (Steindachner), eggs were incubated under different photoperiods to examine the effect of photoperiod on incubation. The eggs from two fish were incubated under five artificial photoperiods: constant dark (D), constant light (L) from 06:00 hours and 6, 10 and 14 h of light from 06:00 hours. The eggs from seven other fish were incubated under a natural photoperiod. Different spawning times (21:00 , 01:00 hours) and different photoperiods combined to give the start of the dusk photoperiod change after 11,23 h of incubation. Constant light or applying the dusk photoperiod change after ,20 h of incubation appeared to extend the hatching period. The mean hatching period for groups of eggs incubated in darkness or that received the dusk photoperiod change after ,19 h of incubation (n=8 different groups) was 2 h 15±10 min, which was significantly lower (P<0.05) than the mean hatching period of 4 h±37 min for groups that did not receive the dusk photoperiod change or that received the dusk photoperiod change after ,20 h of incubation (n=9 groups). However, despite these differences, the majority of the eggs hatched during a 2,3 h period from 17 to 20 h of incubation, and a sigmoid regression (r2=0.9) explained the relationship between percentage hatch and hours of incubation for all photoperiod groups. [source] | ||||||||||