Weeks Of Light Exposure Research Articles

Effects of artificial light with different spectral composition on eye axial growth in juvenile guinea pigs.

The purpose of the study was to investigate the effect of artificial light with different spectral composition and distribution on axial growth in guinea pigs. Three-week-old guinea pigs were randomly assigned to groupsexposed to natural light, low color temperature light-emitting diode (LED) light, two full spectrum artificial lights (E light and Julia light) and blue light filtered light with the same intensity. Axial lengths of guinea pigs'eyes were measured by A-scan ultrasonography prior to the experiment and every 2 weeks during the experiment. After light exposure for 12 weeks, retinal dopamine (DA), dihydroxy-phenylacetic acid (DOPAC) levelsand DOPAC/DA ratio were analyzed by high-pressure liquid chromatography electrochemical detection and retinal histological structure was observed. Retinal melanopsin expression was detected using Western blot andimmunohistochemistry. After exposed to different kinds of light with different spectrum for 4 weeks, the axial lengths of guinea pigs' eyes in LED group and Julia light group were significantly longer than those of naturallight group. After 6 weeks, the axial lengths in LED light group were significantly longer than those of E light group and blue light filtered group. The difference between axial lengths in E light group and Julia light groupshowed statistical significance after 8 weeks (p<0.05). After 12 weeks of light exposure, the comparison of retinal DOPAC/DA ratio and melanopsin expression in each group was consistent with that of axial length. Inguinea pigs, continuous full spectrum artificial light with no peak or valley can inhibit axial elongation via retinal dopaminergic and melanopsin system.

Evaluation of Light-Emitting Diodes' Effects on the Expression Level of P53 and EGFR in the Gingival Tissues of Albino Rats.

Background and objectives: The light-curing unit is considered an essential piece of equipment in every dental office. This study was conducted to evaluate the effect of Light-Emitting Diodes (LEDs) by the light cure (LC) device on gingival tissues of albino rats histologically and by regarding the expression of P53 and epidermal growth factor receptor (EGFR). Materials and methods: Gingival tissues of the rats were exposed to LEDs for 30 s with an interval of 30 s for periods of 2 and 5 min and were examined after two and four weeks of light exposure. After the set time, histological sections were studied and the P53 and EGFR expressions were evaluated immunohistochemically and by molecular methods. Results: Mild hyperplasia and mild inflammatory response were detected in higher rates after two weeks of exposure when compared to 4 weeks postexposure. Whereas fibrosis was found at a higher rate after four weeks than that found after two weeks postexposure, parakeratosis was seen only in the group that was exposed for 5 min to LC and when biopsies were taken after 2 weeks. We found that the immunohistochemical expression of P53 was not changed. Similarly, the alteration of EGFR expression was statistically nonsignificant (p > 0.05) when compared to the control group. The data obtained from the qRT-PCR reaction was analyzed using the comparative CT (2−ΔΔCT) method. Statistically, there was no significant difference in the expression of EGER and P53 gene transcripts. Conclusions: LED causes no serious alteration in P53 and EGFR expression, and only trivial histopathological changes occurred, most of which recovered after a 4-week interval.

Optimising the settlement and hatchery culture of Saccharina latissima (Phaeophyta) by manipulation of growth medium and substrate surface condition

The phaeophyte macroalga Saccharina latissima is gaining economic importance as an aquaculture crop. To decrease costs associated with the hatchery, the time required for meiospores to develop into sporophytes ready for outplanting must be minimised and survivorship maximised. The settlement and juvenile development of S. latissima was examined in a series of experimental manipulations. It was determined that (1) Meiospore settlement should be conducted in the dark in nutrient-enriched medium. (2) Continued nutrient enrichment in the hatchery increased growth and survival of the developing sporophytes. (3) It is best to use the diatom inhibitor germanium dioxide only during settlement and the first week of light exposure, rather than continuously or not at all. This treatment leads to the highest survival rate and sporophyte length. (4) Pre-treating the settlement surface with a commercial yeast extract can increase settlement and early development size; however, over-application can be highly detrimental leading to reduced survival, size and patchy growth.

Residual disinfection with N-halamine based antimicrobial paints

An N-halamine acrylamide monomer was copolymerized with the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid to produce water-dispersible/soluble polymers. The polymers were added into a water-based latex paint and the treated paints were rendered antimicrobial upon chlorination with dilute household bleach. The chlorinated paints were exposed to fluorescent and ultraviolet light for several periods of time. The bound chlorine on the polymers was remarkably stable and the remaining chlorine on the treated paints after several weeks of light exposure was sufficient to provide 6-log inactivations of both Gram-positive and Gram-negative bacteria within 5–10min of contact time. The samples exposed light could be rechlorinated to their initial chlorine loadings, indicating that the polymers were also very stable toward light irradiation. This study describes an effective approach to prepare antimicrobial surfaces providing long-term disinfection.

Stimulatory Effect of Morning Bright Light on Reproductive Hormones and Ovulation: Results of a Controlled Crossover Trial

Objectives:Studies have shown a shortening of the menstrual cycle following light exposure in women with abnormally long menstrual cycles or with winter depression, suggesting that artificial light can influence reproductive hormones and ovulation. The study was designed to investigate this possibility.Design:Placebo-controlled, crossover, counterbalanced order.Setting:Medical centres and participants' homes in Novosibirsk (55°N), Russia.Participants:Twenty-two women, aged 19–37 years, with baseline menstrual cycle length 28.1–37.8 d and no clinically evident endocrine abnormalities completed the study. The study lasted for two menstrual cycles separated by at least one off-protocol cycle.Interventions:During one experimental cycle, bright light was administered at home for 1 wk with a light box emitting white light at 4,300 lux at 41 cm for 45 min shortly after awakening. During the other experimental cycle, dim light was <100 lux at 41 cm with a one-tube fluorescent source.Outcome Measures:Blood samples and ultrasound scans were obtained in the afternoon before and after the week of light exposure, on day ∼7 and 14 after menstruation onset. Further ultrasound scans after day 14 documented ovulation. Serum was assayed for thyroid-stimulating hormone (TSH), prolactin (PRL), luteinizing hormone (LH), follicle-stimulating hormone (FSH), and estradiol (E2).Results:Concentrations of PRL, LH, and FSH were significantly increased with bright versus dim light exposure, as was follicle size (ANOVA, intervention × day, p = 0.0043, 0.014, 0.049, and 0.042, respectively). The number of ovulatory cycles increased after exposure to bright compared to dim light (12 versus 6 cycles, Wilcoxon tied p = 0.034).Conclusions:Morning exposure to bright light in the follicular phase of the menstrual cycle stimulates the secretion of hypophyseal reproductive hormones, promotes ovary follicle growth, and increases ovulation rates in women with slightly lengthened menstrual cycles. This might be a promising method to overcome infertility.

Light therapy in bulimia nervosa: a double-blind, placebo-controlled study

The effects of light therapy on food intake and affective symptoms of bulimia nervosa (BN) were examined in a double-blind study. Eighteen women who met DSM-III-R criteria for BN were randomly assigned to receive either 2500 lux of bright light (experimental condition) or < 500 lux of dim light (placebo condition) daily in the early evening for a 1-week period. The Structured Interview Guide for the Hamilton Depression Rating Scale-Seasonal Affective Disorder Version (SIGH-SAD), the Beck Depression Inventory (BDI), and the Bulimic Symptoms Checklist were administered to subjects before light exposure, after 1 week of light exposure, and after 7 days of withdrawal of light exposure. Throughout the study, the Profile of Mood States and the Daily Binge Record were completed daily. Compared with subjects in the dim light condition, subjects in the bright light condition showed a significant improvement in depressed mood during light exposure, as measured by both the BDI and the SIGH-SAD. There was a return to pretreatment levels of depression after withdrawal of light exposure. No changes in depression were noted in the placebo group. No effect of light therapy was found on the frequency, size, or content of binge-eating episodes. The results are discussed in terms of the physiological processes associated with light therapy and seasonal affective disorder that may underlie the affective and food intake symptoms of BN.

Transient induction of the glial intermediate filament protein gene in Müller cells in the mouse retina.

The glial intermediate filament protein (GFAP) gene is not normally expressed by retinal Müller cells but it is transcriptionally activated following photoreceptor degeneration. In the present study, we have examined the relationship between progressive photoreceptor loss and changes in GFAP gene activity in Müller cells. In albino mice with light-induced photoreceptor degeneration, GFAP level was strongly elevated after 2 weeks. GFAP level remained high even after 3 months in light. In situ hybridization studies showed that GFAP transcripts were quite sparse in the first week but increased dramatically after 2 weeks of light exposure. After 4 weeks in constant light, however, little GFAP mRNA was detected in Müller cells. RNA blotting also showed that there was an approximately 20-fold increase in GFAP mRNA content at 2 weeks; but at 4 weeks, the RNA content fell to about four-fold higher than the basal level. These results show that GFAP level remains high long after its synthesis, probably as a consequence of low GFAP turnover in the Müller cell cytoskeleton, while GFAP mRNA level rises and declines rapidly due to transient activation of the GFAP gene in Müller cells.

Basic fibroblast growth factor and local injury protect photoreceptors from light damage in the rat

Injection of basic fibroblast growth factor (bFGF) into the eye, intravitreally or subretinally, delays photoreceptor degeneration in inherited retinal dystrophy in the rat, as does local injury to the retina (Faktorovich et al., 1990). To determine whether this heparin-binding peptide or local injury is effective in any other form of photoreceptor degeneration, we examined their protective roles in light damage. Albino rats of the F344 strain were exposed to 1 or 2 weeks of constant fluorescent light (115-200 footcandles), either with or without 1 microliter of bFGF solution (1150 ng/microliters in PBS) injected intravitreally or subretinally 2 d before the start of light exposure. Uninjected and intravitreally PBS-injected controls showed the loss of a majority of photoreceptor nuclei and the loss of most inner and outer segments after 1 week of light exposure, while intravitreal injection of bFGF resulted in significant photoreceptor rescue. The outer nuclear layer in bFGF-injected eyes was two to three times thicker than in controls, and the inner and outer segments showed a much greater degree of integrity. Following recovery in cyclic light for 10 d after 1 week of constant light exposure, bFGF-injected eyes showed much greater regeneration of photoreceptor inner and outer segments than did the controls. bFGF also increased the incidence of presumptive macrophages, located predominantly in the inner retina, but the evidence suggests they are not directly involved in photoreceptor rescue. Subretinal injection of bFGF resulted in photoreceptor rescue throughout most of the superior hemisphere in which the injection was made, with rescue extending into the inferior hemisphere in many of the eyes. Remarkably, the insertion of a dry needle or injection of PBS into the subretinal space also resulted in widespread photoreceptor rescue, extending through 70% or more of the superior hemisphere, and sometimes into the inferior hemispheres. This implicates the release and widespread diffusion of some endogenous survival-promoting factor from the site of injury in the retina. Our findings indicate that the photoreceptor rescue activity of bFGF is not restricted to inherited retinal dystrophy in the rat, and that light damage is an excellent model for studying the cellular site(s), kinetics, and molecular mechanisms of both the normal function of bFGF and its survival-promoting activity. Moreover, the injury-related rescue suggests that survival-promoting factors are readily available to provide a protective role in case of injury to the retina, presumably comparable to those that mediate the "conditioning lesion" effect in other neuronal systems.

Nitrosoheme Pigment Formation and Light Effects on Color Properties of Semidry, Nonfermented and Fermented Sausages

Development of the nitrosoheme pigment responsible for visual color properties was studied in the preparation of cured, semidry nonfermented and fermented sausages. Color stability of vacuum packaged sausages differing in pH was also evaluated during 6 weeks of light exposure, and after 6 weeks in dark storage. Total pigment conversion to nitrosoheme increased (P<0.05) during 9.75 h of fermentation at 38°C. The maximum pigment conversion attained upon heat processing to 60°C appeared dependent on prior nitrosoheme formation during fermentation. Judd-Hunter tristimulus coordinates of semidry sausages showed higher (P<0.05) initial +a (redness) values when the pH was 4.85 or 4.65 as compared to pH 5.30 or 6.00. During 6 weeks of light exposure, sausage pH, and time in display were significant factors for each color property. By the fourth and sixth weeks of light exposure, nonfermented sausages (pH 6.0) had maintained redness characteristics better than all fermented sausages (pH 5.30, 4.85, and 4.65) as shown by higher +a and lower hue angle (θ) values. After 6 weeks of light exposure or dark storage, there were no differences (P>0.05) in any color property or nitrosoheme pigment content for nonfermented sausages. However, light exposure, as compared to dark storage, altered (P<0.05) all color properties and reduced (P<0.05) the nitrosoheme pigment content for fermented sausages.

Bright artificial light produces subsensitivity to nicotine

Bright artificial light is a treatment for seasonal depression. Eleven (11) rats were exposed to bright artificial light (11,500 lux) for two consecutive weeks. The thermic response to nicotine was measured prior to light exposure and after one and two weeks of treatment. The thermic response to nicotine at baseline was −1.69 ± 0.25°C (mean ± SEM). The thermic response to nicotine was −0.66 ± 0.12°C (p < 0.002) after one and +0.31 ± 0.14°C (p < 0.000025) after two weeks of light exposure. The change in temperature was different between weeks one and two (p < 0.000025). The exposure of animals to constant light at an intensity of 300 lux did not blunt the hypothermic response to nicotine. These findings suggest that bright artificial light, like other antidepressant treatments, produces subsensitivity of a nicotinic mechanism involved in the regulation of core temperature.