Effect Of Continuous Light Research Articles

Continuous Monochromatic Blue Light Exacerbates High-Fat Diet-Induced Kidney Injury via Corticosterone-Mediated Oxidative Stress.

Excessive illumination is one of the most severe environmental factors that impacts the organism. There is growing evidence that obesity significantly contributes to the onset of chronic kidney disease. However, the effect of continuous light on the kidney and which color can produce an apparent phenomenon remains elusive. In this study, C57BL/6 mice given either a normal diet (LD-WN) or a high-fat diet (LD-WF) were subjected to a light cycle of 12 h of illumination followed by 12 h of darkness for 12 weeks. Meanwhile, 48 high-fat diet mice were given a 24 h monochromatic light exposure of varying colors (white, LL-WF; blue, LL-BF; green, LL-GF) for 12 weeks. As expected, the LD-WF mice showed significant obesity, kidney injury, and renal dysfunction compared with the LD-WN group. LL-BF mice had worse kidney injury than LD-WF mice, including higher Kim-1 and Lcn2. The kidney of the LL-BF group showed marked glomerular and tubular injury, with decreased levels of Nephrin, Podocin, Cd2ap, and α-Actinin-4 compared to LD-WF. LL-BF also reduced the antioxidant capacity, including GSH-Px, CAT, and T-AOC, increased the production of MDA, and inhibited the activation of the NRF2/HO-1 signaling pathway. Furthermore, LL-BF upregulated the mRNA levels of the pro-inflammatory factors Tnf-α, Il-6, and Mcp-1, decreasing the inhibitory inflammatory Il-4 expression. We observed increased plasma corticosterone (CORT), renal glucocorticoid receptors (GR) expression, Hsp90, Hsp70, and P23 mRNA levels. These findings suggested that LL-BF increased CORT secretion and affected glucocorticoid receptors (GR) in comparison to the LD-WF group. Moreover, in vitro research demonstrated that CORT treatment increased oxidative stress and inflammation, which was counteracted by adding a GR inhibitor. Thus, the sustained blue light worsened kidney damage, possibly by inducing elevated CORT and increasing oxidative stress and inflammation via GR.

Effect of Photoblastism on Rice Morphogenesis and Seedling Development

The effect of continuous light and complete dark period on seed germination to first leaf emergence was examined in BRRIdhan71 and BRRIdhan81 in controlled environment at 22 ± 2 ᵒC and 82± 2 % of relative humidity, with or without supplemental LED white light. In the dark, BRRIdhan71 had a germination rate of 97 percent and BRRIdhan81 had a germination rate of 57 percent. Germination was 92 percent in BRRIdhan81 and 77 percent in BRRIdhan71 under photoblastic conditions (Light). The dark and light treatments had a noticeable impact on the percentage of seeds that germinated. Coleoptile was longer in dark than light in BRRIdhan71. In both rice varieties, the light and dark treatments had little effect on the first leaf length, although the first leaf breadth increased noticeably in BRRIdhan81. The growth condition had an impact on root length, seedling fresh weight, and dry weight. Germination percent, coleoptile length, prophyll length, first leaf length, and root length all decreased in BRRIdhan71, whereas germination percent, first leaf length, first leaf breadth, seedling freash, and dry weight all increased significantly in BRRIdhan81.The findings imply that BRRIdhan71 and BRRIdhan81, in particular, responded to photoblastic treatment and predominantly possess photoblastic biocomponents in seed, which affect germination and subsequent growth phases. Rice seed during germinate in the field will light stress if photoblastism is not considered during the development and release of rice varieties for different seasons, such as Aman and Boro, because light affects seeding photomorphogenesis differently in different growth environments.
 Environ. Sci. & Natural Resources, 13(1&2): 43-49, 2020

Effects of Continuous Light (LD24:0) Modulate the Expression of Lysozyme, Mucin and Peripheral Blood Cells in Rainbow Trout

Continuous photoperiod is extensively used in fish farming, to regulate the reproductive cycle, despite evidence suggesting that artificial photoperiods can act as a stressor and impair the immune system. We evaluated the potential effects of an artificial photoperiod on mucus components: lysozyme and mucin, in juvenile rainbow trout (Oncorhynchus mykiss) after exposure for one month to natural photoperiod (LD12:12) or constant light (LD24:0) artificial photoperiod. For each treatment, we assessed changes in peripheral blood cells (erythrocytes and leukocytes) and skin mucus component concentrations. Our results show a decrease in lysozyme concentration, while mucin levels are increased. Similarly, we find elevated monocytes and polymorphonuclears under constant light photoperiod. These findings suggest that LD24:0 regulates lysozyme, mucin, and leukocytes, implying that artificial photoperiods could be a stressful.

Effects of continuous light and light intensity on the growth performance and gonadal development of Nile tilapia

Continuous illumination has been known to exert positive effects by stimulating growth and delaying unwanted maturation in seasonal-temperate farmed fish species like salmonids. However, in tropical fish like Nile tilapia ( Oreochromis niloticus ), some studies exist showing inconsistent results and even fewer data is available regarding the effects of light intensity. To clarify some of the inconsistent results in literature and evaluate the effect of different light intensity levels on growth and sexual maturation in Nile tilapia ( [...]

The Effect of Continuous Light on Growth and Muscle-Specific Gene Expression in Atlantic Salmon (Salmo salar L.) Yearlings.

Photoperiod is associated to phenotypic plasticity of somatic growth in several teleost species, however, the molecular mechanisms underlying this phenomenon are currently unknown. The effect of a continuous lighting (LD 24:0), compared with the usual hatchery lighting (HL) regime, on the growth rate and gene expression of myogenic regulatory factors (MRFs: MyoD1 paralogs, Myf5, and MyoG) myosin heavy chain (MyHC), and MSTN paralogs in the white muscles of hatchery-reared Atlantic salmon yearlings was evaluated over a 6-month period (May–October). The levels of gene expression were determined using real-time PCR. Continuous lighting was shown to have a positive effect on weight gain. MyHC, MyoD1c, MyoD1b, and MSTN1a/b mRNA expression was influenced by the light regime applied. In all the studied groups, a significant positive correlation was observed between the expression levels of MRFs and MSTN paralogs throughout the experiment. The study demonstrated seasonal patterns regarding the simultaneous expression of several MRFs. MyoD1a, MyoG, and MyHC mRNA expression levels were elevated in the mid-October, but MyoD1b/c, and Myf5 mRNA levels decreased by the end of this month. In general, the findings showed that constant lighting affected the regulatory mechanisms of muscle growth processes in salmon.

Effect of continuous light on leaf wax isotope ratios in Betula nana and Eriophorum vaginatum: implications for Arctic paleoclimate reconstructions

Reconstructions of climate using leaf wax D/H ratios (δDwax) require accounting for the apparent isotopic fractionation (εapp) between plant source water and waxes. There have been conflicting publications on whether plants in the Arctic growing under 24-hour continuous light, fractionate less than temperate and tropical plants. In this study, we examine the effect of diurnal light (DL) versus 24-hour continuous light (CL) on the isotopic composition of leaf n-alkanes and n-acids in greenhouse experiments using two common Arctic plants (Eriophorum vaginatum, or tussock cottongrass and Betula nana, or dwarf birch). For E. vaginatum, the δDwax values of various wax homologues were 5–11‰ more positive for CL plants relative to their DL counterparts, whereas for B. nana, CL waxes were 3–24‰ more negative, suggesting that daylight length is not a unifying control on leaf wax D/H ratios of Arctic plants. The δ13Cwax of B. nana was more negative for plants grown in continuous light compared to diurnal light, reflecting lower water-use efficiency, associated with prolonged stomatal opening in the CL treatment. We modeled the impact of increasing stomatal conductance and effective flow path lengths (mimicking variable leaf morphologies) on the isotopic composition of leaf waters (δDlw) and find that variations in leaf-water enrichment may explain the variable δDwax responses seen between E. vaginatum and B. nana. We suggest that between-species differences in the δDlw response to light, and differences in the utilization of stored carbohydrates, were important for governing δDwax. Our greenhouse results suggest that Arctic plant leaf waxes do not consistently display reduced εapp values as a result of 24-hour day light, providing additional support for field observations.

Effect of continuous light on diurnal rhythms in Cyanothece sp. ATCC 51142

BackgroundLife on earth is strongly affected by alternating day and night cycles. Accordingly, many organisms have evolved an internal timekeeping system with a period of approximately 24 hours. Cyanobacteria are the only known prokaryotes with robust rhythms under control of a central clock. Numerous studies have been conducted to elucidate components of the circadian clock and to identify circadian-controlled genes. However, the complex interactions between endogenous circadian rhythms and external cues are currently not well understood, and a direct and mathematical based comparison between light-mediated and circadian-controlled gene expression is still outstanding. Therefore, we combined and analyzed data from two independent microarray experiments, previously performed under alternating light-dark and continuous light conditions in Cyanothece sp. ATCC 51142, and sought to classify light responsive and circadian controlled genes.ResultsFourier Score-based methods together with random permutations and False Discovery Rates were used to identify genes with oscillatory expression patterns, and an angular distance based criterion was applied to recognize transient behaviors in gene expression under constant light conditions. Compared to previously reported mathematical approaches, the combination of these methods also facilitated the detection of modified amplitudes and phase-shifts of gene expression. Our analysis showed that the majority of diurnally regulated genes, essentially those genes that are maximally expressed during the middle of the light and dark period, are in fact light responsive. In contrast, most of the circadian controlled genes are up-regulated during the beginning of the dark or subjective dark, and are greatly enriched for genes associated with energy metabolism. Many of the circadian controlled and light responsive genes are found in gene clusters within the Cyanothece sp. ATCC 51142 genome. Interestingly, in addition to cyclic expression patterns with a period of 24 hours, we also found several genes that oscillate with an ultradian period of 12 hours, a novel finding among cyanobacteria.ConclusionWe demonstrate that a combination of different analytical methods significantly improved the identification of cyclic and transient gene expression in Cyanothece sp. ATCC 51142. Our analyses provide an adaptable and novel analytical tool to study gene expression in a variety of organisms with diurnal, circadian and ultradian behavior.

Effects of photoperiod and exercise on growth, liver size, and age at puberty in farmed Atlantic cod (Gadus morhua L.)

Abstract Sexual maturation in Atlantic cod (Gadus morhua) results in loss of appetite and weight during spawning, leads to increased production time required to reach desired harvest size, and results in greater mortality and reduced food conversion efficiency. Thus, methods to stop or delay maturation are urgently needed. In the present study, the effect of continuous light (LL) treatment on maturation was tested in combination with different exercise levels in seawater tanks compared with controls under natural light. LL treatment in lightproof tanks arrested gonadal development for at least 8 months. Exercising Atlantic cod by forcing them to swim with 0, 0.5, or 1 body length per second from the summer solstice had no effect on incidence of maturation either under natural light or under LL. Growth was enhanced in the LL groups compared with the NL groups, mainly as a result of the weight loss of the NL groups during spawning.

Effect of light period on egg-discharge of gametophyte clones of Undaria pinnatifida (Phaeophyta)

A sporeling culture method using gametophyte clones developed in the early 1990s led to egg discharge occurring in the dark 5 min after the start of the dark period under growth under a 11:13 L-D photoperiod. The course of egg discharge could be disturbed by light, with irradiance as low as 5-6 mu mol photon m(-2) s(-1) causing 75-80% of the discharged eggs to detach from the oogonia and consequently to die within several hours. In order to enhance outgrowth rate of young sporophytes, a study was conducted to test the effect of controlling darkness in the period 2-3 h after dusk. When the slides were transferred from the standard 11:13 L-D regime to continuous light, eggs were discharged 5 min after the end of the light phase and peaked 5-l5 min later on first day after transfer, indicating that the female gametes "remember" the light-dark regime. This suggests the existence of an endogenous circadian rhythm. During the second and third days, very few eggs were discharged throughout the 11 h of the normal light phase of the L-D regime, indicating the inhibitory effect of continuous light and that the rhtyhm is easily damped by light.

Specific binding of melatonin to purified cell nuclei from mammary gland of swiss mice: day-night variations and effect of continuous light.

Melatonin binding sites were characterized in the nuclei of mouse mammary glands. The specific binding of 2-125I-iodomelatonin by homogenates of purified mammary gland cell nuclei was found to be rapid, reversible and saturable. Binding of 125I-melatonin exhibited day-night variations with the highest binding affinity observed during the dark period and the lowest affinity at midday. However, when the animals were maintained under continuous light exposure, binding of 125I-melatonin to cell nuclei showed a higher affinity than the daytime values found in animals maintained in normal photoperiod. Scatchard analysis of the binding data revealed the existence of a significant night-day variation in the binding kinetics, compatible with the existence of two classes of binding sites: a high-affinity binding site expressed during the night, with KD = 185 +/- 36 pm and a binding capacity of 6.24 +/- 0.4 fmol/mg protein, and a low-affinity site with KD = 562 +/- 57 nm and Bmax = 7.56 +/- 0.49 pmol/mg protein during the day. Interestingly, after 2 wk of continuous exposure to light, the animals killed at an equivalent midday time showed a significant increase in binding affinity, with KD = 1.43 +/- 0.2 nm and Bmax = 24.75 +/- 3.5 fmol/mg protein. Displacement experiments show an IC50 value compatible with the affinity constants obtained in the saturation experiments. These results indicate that the low-affinity binding site may be saturated by the high levels of melatonin found in the mouse mammary gland, and sustain the hypothesis of a circadian regulation of these melatonin binding sites by the photoperiod.

Effects of continuous light and melatonin treatment on energy metabolism of the rat.

Melatonin affects food intake, body mass and adiposity of several mammals, but the effects of melatonin on energy metabolism remain largely unknown. This study investigated subacute effects of persistent melatonin treatment and continuous light on carbohydrate and fat metabolism of rat liver and kidney. The male and female rats (no.=40) were maintained either in 12L:12D photoperiod or in constant light. Half the rats in both lighting conditions were treated with continuous-release melatonin implants. Liver lipid concentrations, liver and kidney glucose-6-phosphatase, glycogen phosphorylase and lipase esterase activities, glycogen contents as well as plasma T4, T3, insulin, glucose and melatonin concentrations were determined. There was clear sexual dimorphism in the responses to exogenous melatonin and constant light. Continuous light stimulated carbohydrate metabolism of rat liver. Exogenous melatonin enhanced utilization of liver carbohydrates but suppressed hepatic lipolysis. Changes in normal circulating melatonin concentrations led to enhanced utilization of kidney carbohydrates supporting a role for melatonin in renal function. Both exogenous melatonin and constant light seem to have a strong regulatory effect on rat energy metabolism.

The Effect of Continuous Light on Refractive Error and the Ocular Components of the Rat

Phototoxic induced degeneration of the rat retina is a well-documented phenomenon resulting in losses of photoreceptors and their cell bodies, and an overall retinal thinning. This process may serve as a test of the hypothesis that the retinoscopic reflex originates from the inner limiting membrane of the retina. Retinal thinning should produce myopia in the absence of any other ocular component changes in a stable, mature eye if the inner limiting membrane model is correct. Phototoxic retinal degeneration was induced in 10 albino rats by exposure to 19 days of continuous light (1,800 cd m−2). Another 10 albino rats exposed to 12-hr on/12-hr off cycled light served as controls. Before and after the exposure to constant light, measures were made of refractive state by cycloplegic retinoscopy, corneal curvature and lens curvature by Purkinje image photography, and axial length of the globe by A-scan ultrasonography.Comparing pre- to post-exposure values, phototoxic degeneration resulted in a mean (±s.d.) myopic shift of −5.10±2.12 D (P<0.002). The corneal curvature also steepened significantly (0.17±0.11 mm, equivalent to −6.0 D;P<0.004), while the posterior curvature of the crystalline lens flattened by 0.21±0.22 equivalent mm (P<0.027), and the axial length shortened by 0.11±0.11 equivalent mm (all tests Wilcoxon signed-rank;P<0.025). Phototoxic rats underwent a mean retinal thinning of 49.6 μcompared to controls (Kruskal-Wallis test;P<0.0008). No refractive or ocular parameters changed significantly in the controls. Phototoxic degeneration in the rat has optical consequences beyond simple retinal thinning. The size of the eye and the curvature of refractive surfaces can be altered in a mature eye well after the completion of development. The multiple changes which occur prevent phototoxic retinal thinning from serving as a test of the inner limiting membrane model for retinoscopic reflections.

Effects of light and temperature on seed germination of Poa pratensis from high latitudes

One‐to‐three‐year‐old seed of Poa pratensis "Lavang”;, “Leikra”; and “Ryss”; was germinated under various temperature and light regimes on a thermogradient plate and on paper or in soil in phytotron compartments. While the optimal constant temperature for germination of Lavang and Leikra in 12 h light/12 h dark cycles was around 16°C, Ryss germinated nearly 100% over the 10–28°C temperature range. Compared with constant temperatures, daily fluctuations, even at the small amplitude 18/15°C, stimulated germination of Lavang and Leikra. Dark germination was inferior to germination in light/ dark cycles at constant temperatures of 15°C and higher, but light showed no advantage at alternating temperature. Continuous light inhibited germination regardless of light source (fluorescent, incandescent or natural). The stimulating effect of daily light/dark cycles increased, but the inhibiting effect of continuous light decreased with increasing seed age. It is concluded that seed of Poa pratensis ought to be covered by a 0.5–1.0 cm soil layer when sown in a northern environment involving continuous light and low soil temperatures.

Effects of continuous light, continuous darkness and pinealectomy on pineal-thyroid-gonadal axis of the female Indian palm squirrel, Funambulus pennanti.

Effects of continuous light (CL; 24L:0D), continuous darkness (CD; 24D:0L) and pinealectomy (Px) were tested on pineal-thyroid-gonadal axis of a tropical seasonally breeding rodent, Funambulus pennanti during its sexually active reproductive phase (February-March). CL had no effect on pineal, thyroid and ovarian functions as judged by weight, plasma level of thyroxine (T4) and estradiol (E2). However, CD reduced significantly thyroid and ovarian weight and plasma T4, and E2 levels. Px was stimulatory for thyroid and ovarian functions under normal photoperiod, and under CL, Px significantly increased thyroid and ovarian weights with no observable changes in their hormonal levels. Px under CD condition prevented the reduction in thyroid and ovarian weights but the hormonal levels were increased. These results suggest that CD could be a effective stimulator for the pineal function and increased pineal activity in this mammal. The inhibitory effect of CD on thyroid and ovarian functions could be due to the increased pineal activity in term of induced melatonin by CD itself.

Effects of continuous light on experimental refractive errors in chicks

SummaryIt is possible to induce ametropias in young chicks either by depriving the developing eye of clear form vision with a translucent goggle or by defocusing the retinal image with convex or concave lenses. The refractive properties of the developing chick eye are also altered by raising young birds in a continuous light environment. The effects of superimposing form deprivation or defocus treatments on chicks raised in continuous light are unclear. Newly hatched (n = 31) chicks were raised for 2 weeks under continuous light while wearing either translucent goggles or + 10 or − 10 diopter (D) lenses over one eye. Refractive states, corneal curvature and intraocular dimensions were measured periodically by retinoscopy, keratometry and A‐scan ultrasound. The birds were sacrificed after 2 weeks and the eyes removed and measured with calipers. Under continuous light, all eyes treated with translucent goggle and − 10D lens developed moderate myopia (− 2.6 ± 0.5 D and − 1.4 ± 0.3 D, respectively) by day 4. The eyes treated with a + 10 D lens developed moderate hyperopia (+ 4.8 ± 0.5 D) at day 4. Corneal curvatures of all treated eyes were slightly, but significantly, larger than contralateral control eyes by day 4. After 2 weeks of goggle or lens application, all the treated eyes were hyperopic due to corneal flattening. But the eyes treated with a goggle or a − 10 D lens still showed relative myopia compared to the fellow eyes (treated minus untreated = − 3.8 ± 0.4 D and − 2.8 ± 0.4 D, respectively), and the eyes treated with a + 10 D lens showed more hyperopia than fellow eyes (treated minus untreated = + 5.1 ± 0.6 D). Compared with the control eyes, the axial length (mainly vitreous chamber depth) was slightly, but significantly, increased in the eyes treated with a goggle or a − 10 D lens, and the axial length decreased slightly in the eyes treated with + 10 D lens. The results suggest that form deprivation and retinal defocus (induced by ± 10 D lenses) could still induce experimental refractive errors (myopia and hyperopia) in chicks kept under continuous light, but the effects of form deprivation and retinal defocus were partially suppressed by continuous light.

Effects of continuous light on experimental refractive errors in chicks

It is possible to induce ametropias in young chicks either by depriving the developing eye of clear form vision with a translucent goggle or by defocusing the retinal image with convex or concave lenses. The refractive properties of the developing chick eye are also altered by raising young birds in a continuous light environment. The effects of superimposing form deprivation or defocus treatments on chicks raised in continuous light are unclear. Newly hatched (n = 31) chicks were raised for 2 weeks under continuous light while wearing either translucent goggles or + 10 or − 10 diopter (D) lenses over one eye. Refractive states, corneal curvature and intraocular dimensions were measured periodically by retinoscopy, keratometry and A-scan ultrasound. The birds were sacrificed after 2 weeks and the eyes removed and measured with calipers. Under continuous light, all eyes treated with translucent goggle and − 10D lens developed moderate myopia (−2.6 ± 0.5 D and − 1.4 ± 0.3D, respectively) by day 4. The eyes treated with a + 10 D lens developed moderate hyperopia (+ 4.8 ± 0.5 D) at day 4. Corneal curvatures of all treated eyes were slightly, but significantly, larger than contralateral control eyes by day 4. After 2 weeks of goggle or lens application, all the treated eyes were hyperopic due to corneal flattening. But the eyes treated with a goggle or a − 10 D lens still showed relative myopia compared to the fellow eyes (treated minus untreated = −3.8 ± 0.4D and −2.8 ± 0.4D, respectively), and the eyes treated with a + 10 D lens showed more hyperopia than fellow eyes (treated minus untreated = +5.1 ± 0.6D). Compared with the control eyes, the axial length (mainly vitreous chamber depth) was slightly, but significantly, increased in the eyes treated with a goggle or a −10D lens, and the axial length decreased slightly in the eyes treated with +10D lens. The results suggest that form deprivation and retinal defocus (induced by ±10D lenses) could still induce experimental refractive errors (myopia and hyperopia) in chicks kept under continuous light, but the effects of form deprivation and retinal defocus were partially suppressed by continuous light.

Effects of continuous light and short-day photoperiod on smolting, seawater survival and growth in Atlantic salmon ( Salmo salar)

Duplicate groups of 1-year-old Atlantic salmon were exposed to 5–7 weeks of short days (LD 8.15:15.45) with artificial light, followed by a period of continuous light (LL) for 3 months (A), 2 months (B) or 1 month (C) before transfer to sea cages. Duplicate groups were also exposed to a 2-week period of LD 8.15:15.45, followed by a period of continuous light for 2 months (D). Comparisons were made with fish that were reared under natural light conditions from October onwards (F) and continuous light (E) only. Fish from all groups were transferred to sea cages on 9 June and their survival and growth were monitored until 31 October. There was a significant ( P < 0.001) interaction between light regime and time for all smolt characters measured. Development of smolt colouration, decrease in condition factor, increases in gill Na-K-ATPase activity and the ability to regulate plasma Na + after 24 h in full-strength sea water, indicated that the fish in groups A, B and C completed smoltification 6–8 weeks after the end of the short-day periods. No decrease in the condition factor was recorded for fish in groups D and E. The mortality was 40% for group A and 34% for group B, and 15% or less for the other groups. Groups A and B had probably lost some of the smolt characters by the time of seawater transfer. The specific growth rate in sea water was 1.5% for group F and for the survivors of groups A and B, 1.4% for group C and 1.2% for groups D and E. In conclusion, a short-day regime of 5–7 weeks, followed by continuous artificial light, caused smolt-related changes similar to those found in outdoor-reared fish, whereas this was not so for fish exposed to either a short-day period of only 2 weeks or to continuous artificial light.

Chalcone Synthase from &lt;italic&gt;Camellia sinensis&lt;/italic&gt;: Isolation of the cDNAs and the Organ-Specific and Sugar-Responsive Expression of the Genes

Three full-length cDNAs (CHS1, CHS2 and CHS3) encoding chalcone synthase (CHS; EC 2.3.1.74) were isolated from young leaves of Camellia sinensis. Each cDNA encoded 389 amino acid residues, which showed 93-96% identity to one another. Oligonucleotides were synthesized on the basis of the 5'-untranslated sequences of the cDNAs and their corresponding transcripts could be distinguished. The CHS1, CHS2 and CHS3 transcripts were abundant in the leaves and stems. After an initial treatment with water in darkness, the transcripts fell to very low levels in the young leaves. These levels were increased by a subsequent treatment with fructose, sucrose or maltose in darkness, and they increased still further upon a treatment with glucose, sucrose or maltose under continuous light. These results indicate that the CHS1, CHS2 and CHS3 transcripts are expressed in various organs and respond to sugars in young leaves in a similar manner. The effect of continuous light is also discussed.

Effect of Continuous Light on the Circadian Rhythms of Running-Wheel Activity and Body Temperature in Spontaneously Hypertensive Rats

The circadian rhythms of running-wheel activity and body temperature in a strain of spontaneously hypertensive rats (Aoki) and a strain of normotensive rats (Wistar Kyoto) were analysed. When the rats were exposed to continuous light, the free-running rhythm of activity persisted for more than 30 days in the hypertensive rats, but for only 16–17 days at most in the normotensive ones. The rigidity of the circadian rhythm of activity, judged by comparison with the cycle of light and dark of the initial conditions, was greater in the hypertensive rats and the activity time was longer. Body temperatures were measured rectally at 4-hour intervals in both strains of rats and under both types of lighting conditions. The circadian rhythm of body temperature under continuous illumination was shorter in the hypertensive rats, but its amplitude was larger. Thus the nature of the circadian oscillating system differs in these two strains.

Circadian rhythm of vasopressin levels in cerebrospinal fluid of the fetus: effect of continuous light.

We have measured the concentrations of vasopressin in sequential samples of cerebrospinal fluid (CSF) obtained from fetal lambs between 108 and 130 days gestation. There was a clear and significant (F = 4.46; P less than 0.005) rhythm in vasopressin concentrations in the CSF of nine fetuses, characterized by a mean trough value of 19.4 +/- 6.4 pg/ml (mean +/- SD) at 0200 h and a peak value of 41.1 +/- 28.0 pg/ml at 1400 h. The mean cycle length was 23.2 +/- 1.7 h, with the majority (greater than 80%) of peak concentrations found during daylight hours. There were no concurrent fluctuations in concentrations of vasopressin in plasma or Na, K, Cl, or osmolality in CSF. To examine the relationship between environmental cycles of light and darkness and rhythm of vasopressin concentrations in CSF, pregnant animals were maintained in a constant light environment. In the five fetuses of ewes maintained under these conditions, the rhythm of vasopressin in CSF was markedly damped or not apparent (F = 1.50; P greater than 0.15). These results demonstrate that prominent circadian rhythm of vasopressin in the CSF of the fetus in utero. Despite the fact that the fetus is sequestered from direct influences of the environment, exposure of the pregnant ewe to constant light disrupts the fetal pacemaker that generates the circadian rhythm of vasopressin in CSF. Studies of this rhythm in the fetal lamb, therefore, provide a means to examine the mechanisms of entrainment and assess prenatal influences on circadian organization of the fetus.