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Light Cycle (light + cycle)
Selected AbstractsEffects of Constant, 9 and 16-h Light Cycles on Sperm Quality, Semen Storage Ability and Motile Sperm Subpopulations Structure of Boar SemenREPRODUCTION IN DOMESTIC ANIMALS, Issue 5 2006MM Rivera Contents This study was performed to test the effect that two separate, daily, constant-light regimes of both 9 and 16 h could have on the main parameters of boar-semen quality analysis, as well as on the motile sperm subpopulations structure and the ability of its conservation at 16°C. Results show that both luminous regimes have slight, specific effects on the main parameters of boar-semen quality analysis, as well as on the motile sperm subpopulations structure. Furthermore, the conservation ability at 16°C of boar semen was not significantly different between both photoperiods. When a temporal study was performed, results showed that semen quality and motility parameter changes were stabilized at nearly constant values from the second month of the study to the last month in both luminous regimes, indicating a rapid light-related effect on testicular function. Our results indicate that light regimes oscillating from 9 h daily to 16 h daily are of little importance in the control of boar-semen quality in a farming environment. [source] Chronic Ethanol Disrupts Circadian Photic Entrainment and Daily Locomotor Activity in the MouseALCOHOLISM, Issue 7 2010Allison J. Brager Background:, Chronic ethanol abuse is associated with disrupted circadian rhythms and sleep. Ethanol administration impairs circadian clock phase-resetting, suggesting a mode for the disruptive effect of alcohol abuse on circadian timing. Here, we extend previous studies to explore the effects of chronic forced ethanol on photic phase-resetting, photic entrainment, and daily locomotor activity patterns in C57BL/6J mice. Methods:, First, microdialysis was used to characterize the circadian patterns of ethanol uptake in the suprachiasmatic (SCN) circadian clock and correlate this with systemic ethanol levels and episodic drinking of 10 or 15% ethanol. Second, the effects of chronic forced ethanol drinking and withdrawal on photic phase-delays of the circadian activity rhythm were assessed. Third, the effects of chronic ethanol drinking on entrainment to a weak photic zeitgeber (1 minute of 25 lux intensity light per day) were assessed. This method was used to minimize any masking actions of light that could mask ethanol effects on clock entrainment. Results:, Peak ethanol levels in the SCN and periphery occurred during the dark phase and coincided with the time when light normally induces phase-delays in mice. These delays were dose-dependently inhibited by chronic ethanol and its withdrawal. Chronic ethanol did not impede re-entrainment to a shifted light cycle but affected entrainment under the weak photic zeitgeber and disrupted the daily pattern of locomotor activity. Conclusions:, These results confirm that chronic ethanol consumption and withdrawal markedly impair circadian clock photic phase-resetting. Ethanol also disturbs the temporal structure of nighttime locomotor activity and photic entrainment. Collectively, these results suggest a direct action of ethanol on the SCN clock. [source] EXAMINATION OF DIEL CHANGES IN GLOBAL TRANSCRIPT ACCUMULATION IN SYNECHOCYSTIS (CYANOBACTERIA),JOURNAL OF PHYCOLOGY, Issue 3 2006Rochelle G. Labiosa Phytoplankton in nature must acclimate to a wide range of light conditions resulting from diel light cycles, ocean circulation and mixing, cloud cover, and the variable bio-optical characteristics of the water column. In this study, we used whole-genome cDNA microarrays to investigate the effects of a gradually fluctuating daily light cycle on gene expression in the cyanobacterium Synechocystis sp. strain PCC6803. From these data, we developed a conceptual framework depicting the diel regulation of metabolic pathways in the cell. The framework is focused on potential photoacclimation responses, including the regulation of the photosystems, cell division, and DNA replication. The mRNA abundance of genes involved in many metabolic pathways, and particularly those encoding proteins that function in photosynthesis and DNA replication, changed markedly over the course of the day. The levels of mRNA encoding polypeptides important for the formation of the light-harvesting apparatus, photosystems I and II, and cell division were found in high concentrations during the day. The transcript levels of many genes encoding enzymes involved in anabolic processes also increased considerably during the day. In contrast, transposon transcripts and mRNAs encoding proteins involved in DNA replication, cell wall synthesis, and respiratory activity were not found in high concentrations during the day. Although gradually varying light exposure induced significant changes in transcript accumulation within Synechocystis, the direction of these changes differed between our study and previous studies in which there was an abrupt transition between irradiances. [source] Endogenous melatonin protects L -DOPA from autoxidation in the striatal extracellular compartment of the freely moving rat: potential implication for long-term L -DOPA therapy in Parkinson's diseaseJOURNAL OF PINEAL RESEARCH, Issue 3 2006Gaia Rocchitta Abstract:, We previously showed, using microdialysis, that autoxidation of exogenous L-dihydroxyphenylalanine (l -DOPA) occurs in vivo in the extracellular compartment of the freely moving rat, with a consequent formation of l -DOPA semiquinone (l -DOPA-SQ). In the present study, intrastriatal infusion of l -DOPA (1.0 ,m for 200 min) increased dialysate l -DOPA concentrations (maximum increases up to 116-fold baseline values); moreover, l -DOPA-SQ was detected in dialysates. Individual dialysate concentrations of l -DOPA were negatively correlated with those of l -DOPA-SQ. Co-infusion of N -acetylcysteine (100 ,m) or melatonin (50 ,m) increased l -DOPA (up to 151- and 246-fold, respectively) and decreased l -DOPA-SQ (by about 53% and 87%, respectively) dialysate concentrations. Systemic l -DOPA [25 mg/kg intraperitoneally (i.p.) twice in a 12-h interval] significantly increased striatal baseline dialysate concentrations of l -DOPA and decreased dopamine (DA) and ascorbic acid (AsAc) concentrations, when compared with controls. Following systemic l -DOPA, l -DOPA-SQ was detected in dialysates. Endogenous melatonin was depleted in rats maintained on a 24-h light cycle for 1 wk. In melatonin-depleted rats, systemic l -DOPA induced a smaller increase in dialysate l -DOPA, a greater increase in l -DOPA-SQ formation, and a greater reduction in DA and AsAc dialysate concentrations. Co-administration of melatonin (5.0 mg/kg, i.p., twice in a 12-h interval) with l -DOPA, in control as well as in light-exposed rats, significantly increased dialysate l -DOPA concentrations, greatly inhibited l -DOPA-SQ formation, and restored up to the control values dialysate DA and AsAc concentrations. These findings demonstrate that endogenous melatonin protects exogenous l -DOPA from autoxidation in the extracellular compartment of the striatum of freely moving rats; moreover, systemic co-administration of melatonin with l -DOPA markedly increases striatal l -DOPA bioavailability in control as well as in melatonin-depleted rats. These results may be of relevance to the long-term l -DOPA therapy of Parkinson's disease. [source] The pattern of melatonin secretion is rhythmic in the domestic pig and responds rapidly to changes in daylengthJOURNAL OF PINEAL RESEARCH, Issue 4 2001Anssi Tast The aim of the study was to investigate the capability of pigs to respond to abrupt changes in lighting conditions by means of alterations in circadian melatonin profiles. Sixteen pre-pubertal crossbred male pigs weighing 40,45 kg were housed in individual pens in four temperature- and lighting-controlled climate rooms (four pigs per room). In two rooms there was a light,dark cycle of 16 L:8 D (Group A) and in two other rooms 8 L:16 D (Group B). Under both lighting regimens light intensity at pig eye-level was 220,240 lx during the light phase and less than 7 lx (red light) during the dark phase. The lighting regimens were changed after 2 wks to the opposite regimen and the change was repeated after a further 2 wks, so that animals ended up with the same light cycle with which they started. Blood was sampled at 2-hr intervals for 48 hr spanning each time of change in lighting. A further 24-hr sampling was performed at the end of the experiment (2 wks after the last change) in both groups and 1 wk after the change from short to long day lighting in Group A. On 83/86 occasions, pigs exhibited a clear circadian rhythm in plasma melatonin under both lighting regimens. Pigs responded immediately to the change from long to short day lighting by advancing melatonin secretion to the earlier lights-off time and some pigs were able to extend secretion to the delayed lights-on time. For short to long day changeover there was a small immediate response, with secretion pattern following the previously entrained endogenous rhythm to within 3 hr of the previous lights-on time. After 1 wk commencement of secretion was delayed by up to 2 hr, while after 2 wks some pigs were able to delay commencement of secretion until lights-off or to cease at lights-on. It is concluded that the domestic pig is able to commence adjustment to abrupt changes in photoperiod within a 1-wk acclimatization by altering circadian melatonin secretion. The present study suggests that it may be possible to use simplified lighting regimens instead of stepwise changing lighting programs in commercial piggeries to reduce the influence of season on production. [source] PAR and UV Effects on Vertical Migration and Photosynthesis in Euglena gracilis,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2007Peter Richter Recently it was shown that the unicellular flagellate Euglena gracilis changes the sign of gravitaxis from negative to positive upon excessive radiation. This sign change persists in a cell culture for hours even if subsequently transferred to dim light. To test the ecological relevance of this behavior, a vertical column experiment was performed (max. depth 65 cm) to test distribution, photosynthetic efficiency and motility in different horizons of the column (surface, 20, 40 and 65 cm). One column was covered with a UV cut-off filter, which transmits photosynthetically active radiation (PAR) only, the other with a filter which transmits PAR and UV. The columns were irradiated with a solar simulator (PAR 162 W m,2, UV-A 32.6 W m,2, UV-B 1.9 W m,2). The experiment was conducted for 10 days, normally with a light/dim light cycle of 12 h:12 h, but in some cases the light regime was changed (dim light instead of full radiation). Under irradiation the largest fraction of cells was found at the bottom of the column. The cell density decreased toward the surface. Photosynthetic efficiency, determined with a pulse amplitude modulated fluorometer, was negligible at the surface and increased toward the bottom. While the cell suspension showed a positive gravitaxis at the bottom, the cells in the 40 cm horizon were bimodally oriented (about the same percentage of cells swimming upward and downward, respectively). At 20 cm and at the surface the cells showed negative gravitaxis. Positive gravitaxis was more pronounced in the UV + PAR samples. At the surface and in the 20 and 40 cm horizons photosynthetic efficiency was better in the PAR-only samples than in the PAR + UV samples. At the bottom photosynthetic efficiency was similar in both light treatments. The data suggest that high light reverses gravitaxis of the cells, so that they move downward in the water column. At the bottom the light intensity is lower (attenuation of the water column and self shading of the cells) and the cells recover. After recovery the cells swim upward again until the negative gravitaxis is reversed again. [source] Nonstationary disposition of valproic acid during prolonged intravenous infusion: contributions of unbound clearance and protein bindingBIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 6 2001Tori L. Arens Abstract Circadian variations in disposition have been observed for a variety of agents, including anticonvulsants. Valproic acid (VPA), an anticonvulsant used to control generalized and partial seizures, has exhibited diurnal oscillations in steady-state concentrations during long-term administration to humans and non-human primates. The present study was conducted to assess potential diurnal changes in the disposition of VPA during prolonged i.v. infusion in rats. Animals, maintained on a strict 12-h per day light cycle, were equipped with venous cannulae and an arterial microdialysis probe. VPA was administered as a 50-mg/kg loading dose followed by a 42 mg/kg/h infusion for 70 h. Blood and microdialysate samples were obtained at timed intervals after establishment of steady-state throughout two complete light/dark cycles; and total (serum) and unbound (microdialysate) VPA was determined by gas chromatography. Modest oscillations (6,7 h period) in total and unbound VPA were observed; clearance and binding parameters were not different between light and dark periods. However, unbound clearance increased, and unbound fraction decreased, with time over the course of the infusion. These results suggest that time-dependent changes in VPA disposition occur in rats, although oscillations in steady-state concentrations do not appear to be diurnal in nature. Copyright © 2001 John Wiley & Sons, Ltd. [source] EXAMINATION OF DIEL CHANGES IN GLOBAL TRANSCRIPT ACCUMULATION IN SYNECHOCYSTIS (CYANOBACTERIA),JOURNAL OF PHYCOLOGY, Issue 3 2006Rochelle G. Labiosa Phytoplankton in nature must acclimate to a wide range of light conditions resulting from diel light cycles, ocean circulation and mixing, cloud cover, and the variable bio-optical characteristics of the water column. In this study, we used whole-genome cDNA microarrays to investigate the effects of a gradually fluctuating daily light cycle on gene expression in the cyanobacterium Synechocystis sp. strain PCC6803. From these data, we developed a conceptual framework depicting the diel regulation of metabolic pathways in the cell. The framework is focused on potential photoacclimation responses, including the regulation of the photosystems, cell division, and DNA replication. The mRNA abundance of genes involved in many metabolic pathways, and particularly those encoding proteins that function in photosynthesis and DNA replication, changed markedly over the course of the day. The levels of mRNA encoding polypeptides important for the formation of the light-harvesting apparatus, photosystems I and II, and cell division were found in high concentrations during the day. The transcript levels of many genes encoding enzymes involved in anabolic processes also increased considerably during the day. In contrast, transposon transcripts and mRNAs encoding proteins involved in DNA replication, cell wall synthesis, and respiratory activity were not found in high concentrations during the day. Although gradually varying light exposure induced significant changes in transcript accumulation within Synechocystis, the direction of these changes differed between our study and previous studies in which there was an abrupt transition between irradiances. [source] Robust circadian rhythm in heart rate and its variability: influence of exogenous melatonin and photoperiodJOURNAL OF SLEEP RESEARCH, Issue 2 2007GILLES VANDEWALLE Summary Heart rate (HR) and heart rate variability (HRV) undergo marked fluctuations over the 24-h day. Although controversial, this 24-h rhythm is thought to be driven by the sleep,wake/rest,activity cycle as well as by endogenous circadian rhythmicity. We quantified the endogenous circadian rhythm of HR and HRV and investigated whether this rhythm can be shifted by repeated melatonin administration while exposed to an altered photoperiod. Eight healthy males (age 24.4 ± 4.4 years) participated in a double-blind cross-over design study. In both conditions, volunteers were scheduled to 16 h,8 h rest : wake and dark : light cycles for nine consecutive days preceded and followed by 29-h constant routines (CR) for assessment of endogenous circadian rhythmicity. Melatonin (1.5 mg) or placebo was administered at the beginning of the extended sleep opportunities. For all polysomnographically verified wakefulness periods of the CR, we calculated the high- (HF) and low- (LF) frequency bands of the power spectrum of the R,R interval, the standard deviation of the normal-to-normal (NN) intervals (SDNN) and the square root of the mean-squared difference of successive NN intervals (rMSSD). HR and HRV variables revealed robust endogenous circadian rhythms with fitted maxima, respectively, in the afternoon (16:36 hours) and in the early morning (between 05:00 and 06:59 hours). Melatonin treatment phase-advanced HR, HF, SDNN and rMSSD, and these shifts were significantly greater than after placebo treatment. We conclude that endogenous circadian rhythmicity influences autonomic control of HR and that the timing of these endogenous rhythms can be altered by extended sleep/rest episodes and associated changes in photoperiod as well as by melatonin treatment. [source] | |||||||||||||