Effect Of Continuous Light Research Articles

Effects of continuous light on rat parotid gland structure and reactivity

The effects of continuous light on ultrastructural organization and sympathetic secretory responses of the rat parotid gland are reported. After 50 days of continuous light exposure, the fine structure of the parotid gland exhibited features of enhanced secretory activity as judged by the striking development of rough endoplasmic reticulum and Golgi complexes, the depletion of secretory granules and the increased turnover of secretory cells. The secretory responses of parotid gland to isoproterenol revealed that continuous light induced a 30% increase in amylase release. This secretory hyperactivity appears to be related to a postsynaptic supersensitivity of sympathetic fibers of the autonomic nervous system.

The effect of continuous light on prolactin secretion in prepubertal holstein bulls

Effects of 16 (16 light:8 dark) and 8 (8L:16D) h of daily light were compared with continuous light (24L:0D) exposure on prolactin (PRL) concentrations in serum of prepubertal bulls. Concentrations of PRL in serum were 2 to 3 fold greater in bulls exposed to 24L:0D or 16L:8D as compared with 8L:16D. However, PRL concentrations attained a maximum approximately 3 weeks later in calves exposed to 24L:0D than in calves given 16L:8D. Continuous low intensity (11 to 16 lux) lighting supplemented with 16 or 8 h of high intensity (449 to 618 lux) light per day increased PRL concentrations in serum of prepubertal bulls 1.5 to 2.5 fold relative to 8L:16D (470 lux). We found that relative to 8L:16D, 1) photoperiods of 16 or 24 h of light per day increased serum concentrations of PRL in prepubertal bulls; however, the time required to achieve maximum PRL concentrations was longer in animals exposed to 24L:0D, 2) continuous low intensity lighting supplemented with 16 or 8 h of high intensity daily light also increased concentrations of PRL in serum.

Analysis of the operation of the photoperiodic counter provides evidence for hourglass time measurement in the spider miteTetranychus urticae

Photoperiodic induction of diapause in the spider miteTetranychus urticae is the net result of at least two processes: time measurement (the photoperiodic ‘clock’) and the accumulation of the photoperiodic information contained in a sequence of light-dark cycles (the photoperiodic ‘counter’). In this paper an analysis is presented of the operation of the photoperiodic counter in the spider mite. 1. Mites which experienced a sequence of longnight cycles during their entire sensitive period showed 100% diapause; no diapause was observed in continuous darkness. When an increasing number of long-night cycles was applied to the mites against a ‘background’ of continuous darkness, diapause incidence was found to rise steadily: only 3 cycles sufficed to induce diapause in about half the population, whereas a minimal number of 6 cycles was required for 90–100% diapause to be attained. At the test temperature of 18.5°C the sensitive period lasted 11–12 days, comprising the complete post-embryonic developmental period, up to the final moult. Photoperiodic sensitivity was found to vary slightly over the whole sensitive period of the mites, the highest sensitivity being observed around days 3–6. 2. Short-night cycles were also shown to be accumulated, but with an effect opposite to that of long-night cycles. If the mites received a number of short-night cycles before being transferred to a long-night regime, the effect of the short-night cycles had to be levelled first by a number of longnight cycles, before the accumulation of the diapause-inducing effect of the long-night cycles was started. 3. Special attention has been given to the effect of the aperiodic signals continuous light and continuous darkness. It could be shown that continuous light has a slightly reversing effect on diapause induction if applied after a series of long-night cycles; continuous light is more or less ‘neutral’ (i.e. neither reversing nor promoting diapause induction) if it precedes the long-night cycles. 4. In experiments in which the effects of continuous light and continuous darkness were compared it could be shown that continuous darkness is equivalent to one long night: the minimal number of long-night cycles required for diapause induction was found to be one more if the long-night cycles were given after the mites had received continuous light instead of continuous darkness during the first part of the sensitive period. 5. A critical test, based on the photoperiodic counter principle and devised to discriminate between single and repeated nightlength measurements (using nights of 12 h and 36 h long), showed that all nights are counted only once, irrespective of their lengths: all nights longer than the critical nightlength were found to be about equally inductive. This shows that the photoperiodic clock in the spider mite does not operate according to oscillator kinetics: a clock of the oscillator type resets itself in longer dark phases and would have performed two consecutive acts of time measurement in a night of 36 h long. Consequently, the photoperiodic clock inT. urticae is either an hourglass or an instantly damped circadian oscillator, the kinetics of either of which would produce the results observed in the experiments reported here.

Induction kinetics of heat emission before and after photoinhibition in cotyledons of Raphanus sativus

Heat emitted during non-radiative de-excitation was determined in vivo by the photoacoustic method. The dependence of the photoacoustic signal on the length of the pulses (modulation frequency) of the excitation light and the effect of continuous light, which saturates photosynthesis but does not directly contribute to the signal, are described. The induction kinetic of heat emission measured with intact leaves differed only slightly from the induction kinetic of fluorescence (Kautsky effect) detected in parallel. The photoacoustic signal at high modulation frequencies (279 Hz), which represents the signal of heat emission, and the photoacoustic signal at low modulation frequencies (17 Hz), interpreted as a signal of pulsed oxygen evolution superimposed on the heat emission, were measured with leaves before and after photoinhibition. It was demonstrated that after photoinhibition the decrease in fluorescence yield and in photosynthetic activity (here detected as photoacoustic signal at 17 Hz) are paralleled by an increase in the yield of non-radiative deexcitation (photoacoustic signal at 279 Hz). The increase of heat emission, which has been hypothized for photoinhibited leaves, could now be proved by measuring the induction kinetics of the photoacoustic signal.

Biochemical studies on the effects of continuous light on the albino rat retina

The causal mechanism of light damage in the albino rat retina has been investigated. Male and female albino Wistar rats weighing 200–300 g and previously maintained in normal room lighting of approximately 15 hr light (0·85±0·05 × 10 −4 W cm −2) per 9 hr dark cycle were simultaneously exposed continuously to uniform fluorescent light flux of 3·01±0·5 × 10 −3 W cm −2 for a period of 6–18 hr. The animals were killed immediately after exposure and the retinas analysed for their contents of DNA, protein and lipids. There were significant losses of retinal DNA, protein, total lipid and polyunsaturated fatty acids, particularly docosahexaenoic acid. The losses were progressive with duration of exposure. There were also changes in phospholipid subclasses. These results could indicate altered photoreceptor-membrane viability secondary to continuous illumination. The ultimate effect would be the loss of photoreceptor cells with a concomitant loss of normal physiological function. Generally, gender was found to play no significant role, thus excluding possible endocrine interference. It is suggested that lipoperoxidative reactions could account for the observations made in this study. The danger of over-exposure to radiant flux in the tropics is inferred from these observations.

Specificity and Interaction among Auxins, Light, and pH in Rooting of Australian Woody Species in Vitro

Abstract A number of Australian woody species are shown to differ widely in adventitious root production in vitro in response to the type and combination of hormones applied, although the most effective combinations usually included IBA. Shoots of Eremophila lanii F. Muell produced roots on a medium containing cytokinins and no auxin. Two species, Prostanthera striatiflora F.v.M and Correa decumbens F.v.M., required reduced pH and a period of darkness for root induction, whereas these conditions inhibited Grevillea biternata Meissner. There also is an interaction among hormone treatment, media pH, and the effect of continuous light vs. a period of darkness. Chemical names used: 1H-indole-3-butanoic acid (IBA); naphthhalene acetic acid (NAA); indole-3-acetic acid (IAA); B-naphthoxyacetic acid (NOA); 6-furylaminopurine (KIN); N-(phenylmethyl)-1H-purin-6-amine (BA).

Effects of continuous light and dark exposure on hypothalamic thyrotropin-releasing hormone in rats.

The thyrotropin-releasing hormone (TRH) content in whole hypothalamus was measured by specific radioimmunoassay in rats exposed to a daily light-dark cycle (06:00-18:00 light, 18:00-06:00 dark) and in animals exposed to constant light or constant darkness for 12 days. A nyctohemeral variation of hypothalamic TRH was observed in light-dark exposed animals, while this variation was abolished by exposure either to constant light or constant darkness. These data indicate that any study involving hypothalamic TRH determination should be carried out taking into account the diurnal variation and the effect of environmental light exposure.

Effect of continuous light on the incidence of 9,10-dimethyl-1,2-benzanthracene induced mammary tumors in female Holtzman rats

The pineal has been recently implicated in mammary tumorigenesis. Effect of physiological pinealectomy brought about by subjecting female Holtzman rats to permanent lighting (24 h/day) from birth was studied on the incidence of 9,10-dimethyl-1,2-benzanthracene (DMBA) induced mammary tumors. The incidence of adenocarcinoma was 95% in animals maintained in continuous photoperiod in contrast to that (60%) observed in control animals maintained on a light/dark ( 10 14 h ) schedule. Further, the latency period of tumor appearance (61.5 ± 9 days) in the former group was found to be significantly shorter than that seen in the latter group (93.7 ± 8.3 days). Explanations are offered for this difference in the observed incidence.

The effects of continuous light and light intensity on the reproduction rates of twenty-two species of marine phytoplankton

The acclimated reproduction rates of 22 species of marine phytoplankton were measured at 0.01, 0.023, 0.1, and 0.23 ly/min in continuous light and in a 14: 10 h light: dark cycle. Three species that reproduced exponentially at all four light intensities in the 14: 10 LD regime did not reproduce at all in continuous light at any of the light intensities. One species, which reproduced at the two lowest light intensities in the 14: 10 LD regime, failed to reproduce at all in continuous light at any light intensity examined. Seven species reproduced more slowly in continuous light than in the 14: 10 LD regime at most or all light intensities. Four species reproduced at roughly the same rate in both light regimes. Five species reproduced more rapidly in continuous light. No general phylogenetic trend could be discerned from the responses of the species to the different light intensities or to continuous light. In general, species from coastal regions can reproduce as rapidly or more rapidly in continuous light than in a 14: 10 LD cycle, while most species from oceanic regions are harmed by continuous light. A phylogenetic trend in maximum potential reproduction rate is apparent, with diatoms being the fastest, dinoflagellates the slowest, and coccolithophores somewhat intermediate.

Influence of white light on production of aflatoxins and anthraquinones in Aspergillus parasiticus.

The effect of continuous light and continuous darkness on the growth of Aspergillus parasiticus and on the production of aflatoxin, averufin, versicolorin A, and versicolorin C by Aspergillus parasiticus were determined at six different temperatures with six replicates for each experiment. No growth was observed at 15 degrees C in the light, although slight growth was observed at this temperature in the dark. No aflatoxins or anthraquinones were produced in the light or dark at 35 and 40 degrees C, although growth was good at these temperatures. Differences in aflatoxins and anthraquinones for cultures grown in light and in dark were consistent at each temperature. Higher mean quantities of these secondary metabolites were produced in the light at 20 and 25 degrees C; lower mean quantities were produced in the light at 30 degrees C. The ranges of values overlapped considerably, but in all cases the differences between temperatures were significant.

Effect of continuous light on the blood and urinary sugar levels in alloxan diabetic rats.

Continuous light decreases the rise in blood glucose and the excretion of urinary glucose, along with increased urine volume, in alloxan diabetic rats.

Further studies on diurnal changes in small vesicles in sympathetic nerve endings in the mouse pineal and the effects of continuous light on the vesicles--quantitative electron microscopic observations.

Diurnal variations in the number of various types of small granulated and non-granulated vesicles as well as effects of continuous light on the vesicles in sympathetic nerve endings of the mouse pineal were investigated using quantitative electron microscopic techniques. Small granulated vesicles, 40 to 80 nm in diameter, were classified into two categories, type 1 or type 2, according to the size of the granule. Small non-granulated vesicles were also divided into two categories, i.e., spherical and elliptical. Non-granulated vesicles with the long diameter more than twice the shorter one (ranging from 50 to 90 nm in long diameter) were referred to as elliptical vesicles and the other (ranging from 40 to 80 nm in diameter) as spherical vesicles. The number of small vesicles, except for the non-granulated spherical vesicles, varied diurnally in relation to the daily photoperiod. The total vesicle density also exhibited diurnal changes. On the basis of these observations, possible relationships between small vesicles and noradrenaline or serotonin were discussed. Both the diurnal variation in small vesicles and that in the total vesicle density were completely abolished by continuous lighting. Continuous light exposure for various periods until 35 days provoked no apparent changes in small vesicles, except the type 2 granulated vesicles, which were increased in number in response to continuous lighting for about 1 to 3 days.

Effect of continuous light and darkness on the testicular histology of toad (Bufo melanostictus).

Continuous darkness decreases spermatogenesis as well as Leydig cell function whereas continuous illumination suppresses spermatogenesis along with increased Leydig cell activity.

Effect of continuous light on CO2 fixation, chlorophyll content, growth and chloroplast structure in Ceratodon purpureus

Summary In protonemata of Ceratodon, continuous light decreased the rate of CO2 fixation and chlorophyll content calculated on the basis of dry weight. The effect on the chlorophyll content could not be eliminated by adding nutrients to the medium. However, the development of the protonemata and the increase in dry weight were more rapid in continuous than in rhythmic light, and the rate of CO2 fixation was not lower when it was calculated on the basis of the chlorophyll content. The chloroplasts had more lamellae per granum and more starch in continuous than in rhythmic light. The chl a/chl b ratio was lower in the protonemata grown in continuous light, and this difference was accompanied by increased granum size and a higher percentage of chlorophyll-protein complex II.

Effects of continuous light and darkness on the eyes of the troglobitic salamander Typhlotriton spelaeus

Larval Typhlotriton spelaeus collected from five caves in Pulaski Co., Missouri, were kept as larvae or induced to transform in darkness or continuous fluorescent illumination. Larvae maintained in darkness for 215 and 279 days had smaller eyes, smaller rod inner and outer segments, and fewer metaphase figures in the germinative zone of the neural retina than comparable larvae maintained in light (258 lux). Except for visual cell size, differences were small and for each characteristic exceptions were observed. One larva kept in light showed early retinal degeneration comparable to that in transformed adults to T. spelaeus. All larvae exhibited optomotor behavior both before and after the experiment. Among animals induced to transform by L-thyroxin and maintained in darkness 111 to 366 days, visual cell and pigment epithelium degeneration was more extensive and more frequent than in animals kept for the same length of time in light (237-298 lux). In darkness the frequency of animals with retinal degeneration increased between 111 and 366 days. In light some animals exhibited pigment epithelium reduction with normal visual cells, and others had free, pigmented cells in the subretinal space. These effects were not comparable to degeneration in darkness. Eyelids covered the eyes of only a few animals in both light and dark treatments. The extent of eyelid encroachment over the eye greater in darkness than in light. Most animals exhibited optomotor responses after experiments, but responses of animals kept in darkness were impaired in comparison to those of animals kept in light.

Effects of Continuous Light and Darkness, and of Pinealectomy, Adrenalectomy and Gonadectomy on Uptake of <sup>3</sup>H-Serotonin by the Suprachiasmatic Nuclear Region of Male Rats

Rats exposed to continuous light show no significant differences in serotonin (5-HT) uptake by the suprachiasmatic nuclear region (SNR) at 10.00 and 22.00 L, while in continuous darkness, the uptake at 10.00 D is significantly higher than uptake at 22.00 D. In consideration of the role of the suprachiasmatic nucleus in light-mediated control of neuroendocrine activity, this suggests endogenous generation or control of this uptake rhythm. An effect of sham-pinealectomy in decreasing 5-HT uptake was found, but cannot be fully interpreted at this time. The lack of effect of castration or adrenalectomy suggests that these endocrines have little if any direct effect on 5-HT mechanisms in the SNR.

Scoto/photo‐periodic responses of a sub‐tropical finch (Spotted munia) in relation to seasonal breeding cycle

Abstract Effects of continuous light and dark periods and long and ultrashort photoperiods on the gonadal function of a subtropical finch, Spotted munia, hitherto considered “non‐photosensitive”, were studied. This bird seems to be unique in that while gametogenesis and hormone production are stimulated by the continuous or long scoto periods the endogenous rhythm of reproduction continues in constant 24hr or 15hr long daily photoperiod.

Mediterranean Flour Moth:1 Effects of Continuous Light on the Reproductive Capacity 3

Male Mediterranean flour moths, Anagasta kuehniella (Zeller), maintained under continuous illumination (130-140 lux) from the pupal stage onward had a much lower reproductive capacity than males maintained under 12 hours of light alternated with 12 hours of darkness. Factors that could be identified as contributing to reproductive failure included decreased mating, decreased release of sperm from the testes, and failure of much or all the sperm to move from the spermatophore to the female spermathecae.

Influence of Continuous Light on Oöcyte Maturation in Bracon hebetor1

Oocyte maturation in the parasitic wasp Bracon hebetor Say was compared among females reared in continuous light (LL), continuous dark (DD), and alternating light-dark periods (LD). The mean number of mature oocytes in females from LL cultures was twice that of females from LD cultures and almost 3 times that of females from DD cultures. When reared under LD or DD, 84–87% of the females contained 1–9 mature oocytes at emergence, but under LL, 78% of the females had 10–22 mature oocytes. The effect of continuous light on oocyte maturation was independent of the rearing conditions of the larvae as the effect of light or dark on oocyte production and maturation was found to occur in the pupal stage. Because continuous light stimulated oocyte maturation in B. hebetor and decreased the reproductive potential of the host insect, the Indian meal moth, Plodia interpunctella (Hubner), the use of light provides a potential means for developing more effective biological control methods against P. interpunctella.

The influence of daylength and temperature on the testis pterin content of Drosophila littoralis

The testis pterin content is an indicator of the total pterin metabolism of adult Drosophila littoralis. The light-dark cycle 18 : 6 hr (and in some strains also LD 6 : 18) causes a marked decrease in testis pterin content as compared with the effect of continuous light, LD 12 : 12, and continuous darkness. A skeletal rhythm LDLD 1 : 5 : 1 : 17 has an effect similar to that of LD 6 : 18, whereas the skeletal rhythm LDLD 5 : 1 : 17 : 1 corresponds with LD 18 : 6. A shift of the light-dark cycle at eclosion may decrease the pterin content, but never increase it. A model of the effect of daylength on pterin metabolism is constructed. The rate of pterin accumulation in the testis is directly proportional to temperature from about 10 to 23°C, but this correlation is lost at higher or lower temperatures. The decrease in pterin accumulation due to low temperature can be reversed at LD 18 : 6 by increasing the temperature to 23°C for about a week. It is suggested that the low temperature affects only the storage excretion but not the synthesis of the pterins.