Home About us Contact
|
Home About us Contact | ||
|
|
||
Light Stimuli (light + stimulus)
Selected AbstractsCircadian phase entrainment via nonlinear model predictive controlINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 17 2007N. Bagheri Abstract A nonlinear model predictive control algorithm is developed to investigate the phase-resetting properties of robust nonlinear biological oscillators; in particular, those of the circadian rhythm. This pacemaker is an autonomous biochemical oscillator with a free-running period close to 24 h. Research in chronobiology indicates that light stimuli may delay or advance the phase of the oscillator, allowing it to synchronize physiological processes and entrain to the environment. In this paper, a closed-loop optimal phase tracking control algorithm is developed and applied to a mammalian circadian model. The integration of MPC-based light pulses, coupled with environmental light:dark cycles, allows the circadian system to recover phase differences within 1.5 days,a fraction of the natural open-loop simulated mammalian recovery time. Accelerated phase entrainment may alleviate disorders caused by circadian rhythms that are out of phase with the environment, and improve performance. Copyright © 2007 John Wiley & Sons, Ltd. [source] Photosensory Functions of Channelrhodopsins in Native Algal Cells,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2009Oleg A. Sineshchekov Photomotility responses in flagellate alga are mediated by two types of sensory rhodopsins (A and B). Upon photoexcitation they trigger a cascade of transmembrane currents which provide sensory transduction of light stimuli. Both types of algal sensory rhodopsins demonstrate light-gated ion channel activities when heterologously expressed in animal cells, and therefore they have been given the alternative names channelrhodopsin 1 and 2. In recent publications their channel activity has been assumed to initiate the transduction chain in the native algal cells. Here we present data showing that: (1) the modes of action of both types of sensory rhodopsins are different in native cells such as Chlamydomonas reinhardtii than in heterologous expression systems, and also differ between the two types of rhodopsins; (2) the primary function of Type B sensory rhodopsin (channelrhodopsin-2) is biochemical activation of secondary Ca2+ -channels with evidence for amplification and a diffusible messenger, sufficient for mediating phototaxis and photophobic responses; (3) Type A sensory rhodopsin (channelrhodopsin-1) mediates avoidance responses by direct channel activity under high light intensities and exhibits low-efficiency amplification. These dual functions of algal sensory rhodopsins enable the highly sophisticated photobehavior of algal cells. [source] Phosphatidylinositol 4,5-bisphosphate is important for stomatal openingTHE PLANT JOURNAL, Issue 5 2007Yuree Lee Summary Previously, we demonstrated that a protein that binds phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] inhibits both light-induced stomatal opening and ABA-induced stomatal closing. The latter effect is due to a reduction in free PtdIns(4,5)P2, decreasing production of inositol 1,4,5-trisphosphate and phosphatidic acid by phospholipases C and D. However, it is less clear how PtdIns(4,5)P2 modulates stomatal opening. We found that in response to white light irradiation, the PtdIns(4,5)P2 -binding domain GFP:PLC,1PH translocated from the cytosol into the plasma membrane. This suggests that the level of PtdIns(4,5)P2 increases at the plasma membrane upon illumination. Exogenously administered PtdIns(4,5)P2 substituted for light stimuli, inducing stomatal opening and swelling of guard cell protoplasts. To identify PtdIns(4,5)P2 targets we performed patch-clamp experiments, and found that anion channel activity was inhibited by PtdIns(4,5)P2. Genetic analyses using an Arabidopsis PIP5K4 mutant further supported the role of PtdIns(4,5)P2 in stomatal opening. The reduced stomatal opening movements exhibited by a mutant of Arabidopsis PIP5K4 (At3g56960) was countered by exogenous application of PtdIns(4,5)P2. The phenotype of reduced stomatal opening in the pip5k4 mutant was recovered in lines complemented with the full-length PIP5K4. Together, these data suggest that PIP5K4 produces PtdIns(4,5)P2 in irradiated guard cells, inhibiting anion channels to allow full stomatal opening. [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] Reflectance spectra of Munsell standard chips and their appearanceCOLOR RESEARCH & APPLICATION, Issue 3 2008Tarow Indow Abstract In this article, we present the results of analysis by two different methods for representing information in reflectance spectra of Munsell standard chips that relates to their appearance. The spectrum of a chip j is denoted as rj, where , represents wavelength , from 430 to 660 nm with 1 nm intervals. The spectrum of light reflected from a chip j under D65 is rj, × e, where e, represents the spectral power distribution of D65 illumination. In one method, singular value decomposition is applied to a matrix of (rj, × e,). Combining results of this analysis with results of human assessment experiments, we obtain four curves ,0,(H) that represent principal hue components , in Munsell Hue, , = redness, yellowness, greenness, and blueness (Fig. 6). The other method is multiple regression of each (rj, × e,) to activities of three kinds of cones in the retina. From this analysis, we obtain three curves Bq(H) that represent relative involvements of q = L, M, S cone activities in determining the appearance of Munsell Hue (Fig. 10). Two sets of curves, ,0,(H), and Bq(H), are compared with predictions from a model of higher order color mechanism (Fig. 12) that has been proposed on the basis of experiments with light stimuli of wavelength ,. It is found that ,0,(H), and Bq(H) constructed from broadband spectra of Munsell chips are interpretable in terms of this model. © 2008 Wiley Periodicals, Inc. Col Res Appl, 33, 229,237, 2008 [source] Photoswitches: From Molecules to MaterialsADVANCED MATERIALS, Issue 31 2010Maria-Melanie Russew Abstract Small organic molecules, capable of undergoing efficient and reversible photochemical reactions to switch them between (at least) two (meta)stable isomers associated with markedly different properties, continue to impact the materials world. Such photoswitches are being implemented in a variety of materials for applications ranging from optical devices to "smart" polymers. All approaches exploit the photoswitching molecular entities as gates, which translate an incoming light stimulus to trigger macroscopic property changes of the materials. In this progress report, the most promising recent examples in this field are highlighted and put in perspective. Moving from supramolecular systems in solution to surfaces and finally to bulk materials, important design concepts are discussed, emphasizing both the challenges as well as the great promise of such truly advanced materials. [source] Genetic Correlation Between Innate Alcohol Preference and Fear-Potentiated Startle in Selected Mouse LinesALCOHOLISM, Issue 7 2007Gustavo D. Barrenha Background: There is a high rate of co-occurrence between anxiety and alcohol-use disorders in humans that may arise from the inheritance of common genes that increase the risk for both psychiatric disorders. The purpose of this study was to investigate whether a genetic relationship exists between innate alcohol preference and propensity to develop learned fear, using the fear-potentiated startle (FPS) paradigm, in 2 mouse lines selectively bred for high or low alcohol preference. Methods: Alcohol-naïve, male, and female mice from replicate pairs of lines selectively bred for high alcohol preference and low alcohol preference were randomly assigned to a fear-conditioned or control group. Mice in the fear-conditioned group received 20 pairings of a light stimulus and footshock; the control group received the same number of exposures to light and footshock, except that these stimuli were explicitly unpaired. During testing for FPS, acoustic stimuli were presented both in the presence and in the absence of the light stimulus. Results: In both replicate pairs of lines, mice selectively bred for high alcohol preference showed greater FPS than mice selectively bred for low alcohol preference. No sex differences in FPS were found in any line. Control groups did not show FPS. Conclusion: These findings suggest that common genes mediate both innate alcohol preference and propensity to develop learned fear in these selected mouse lines. [source] Developmental Alcohol Exposure Alters Light-Induced Phase Shifts of the Circadian Activity Rhythm in RatsALCOHOLISM, Issue 7 2004Yuhua Z. Farnell Background: Developmental alcohol (EtOH) exposure produces long-term changes in the photic regulation of rat circadian behavior. Because entrainment of circadian rhythms to 24-hr light/dark cycles is mediated by phase shifting or resetting the clock mechanism, we examined whether developmental EtOH exposure also alters the phase-shifting effects of light pulses on the rat activity rhythm. Methods: Artificially reared Sprague-Dawley rat pups were exposed to EtOH (4.5 g/kg/day) or an isocaloric milk formula (gastrostomy control; GC) on postnatal days 4 to 9. At 2 months of age, rats from the EtOH, GC, and suckle control groups were housed individually, and wheel-running behavior was continuously recorded first in a 12-hr light/12-hr dark photoperiod for 10 to 14 days and thereafter in constant darkness (DD). Once the activity rhythm was observed to stably free-run in DD for at least 14 days, animals were exposed to a 15-min light pulse at either 2 or 10 hr after the onset of activity [i.e., circadian time (CT) 14 or 22, respectively], because light exposure at these times induces maximal phase delays or advances of the rat activity rhythm. Results: EtOH-treated rats were distinguished by robust increases in their phase-shifting responses to light. In the suckle control and GC groups, light pulses shifted the activity rhythm as expected, inducing phase delays of approximately 2 hr at CT 14 and advances of similar amplitude at CT 22. In contrast, the same light stimulus produced phase delays at CT 14 and advances at CT 22 of longer than 3 hr in EtOH-treated rats. The mean phase delay at CT 14 and advance at CT 22 in EtOH rats were significantly greater (p < 0.05) than the light-induced shifts observed in control animals. Conclusions: The data indicate that developmental EtOH exposure alters the phase-shifting responses of the rat activity rhythm to light. This finding, coupled with changes in the circadian period and light/dark entrainment observed in EtOH-treated rats, suggests that developmental EtOH exposure may permanently alter the clock mechanism in the suprachiasmatic nucleus and its regulation of circadian behavior. [source] Characterisation of Zea mays L. plastidial transglutaminase: interactions with thylakoid membrane proteinsPLANT BIOLOGY, Issue 5 2010A. Campos Abstract Chloroplast transglutaminase (chlTGase) activity is considered to play a significant role in response to a light stimulus and photo-adaptation of plants, but its precise function in the chloroplast is unclear. The characterisation, at the proteomic level, of the chlTGase interaction with thylakoid proteins and demonstration of its association with photosystem II (PSII) protein complexes was accomplished with experiments using maize thylakoid protein extracts. By means of a specific antibody designed against the C-terminal sequence of the maize TGase gene product, different chlTGase forms were immunodetected in thylakoid membrane extracts from three different stages of maize chloroplast differentiation. These bands co-localised with those of lhcb 1, 2 and 3 antenna proteins. The most significant, a 58 kDa form present in mature chloroplasts, was characterised using biochemical and proteomic approaches. Sequential fractionation of thylakoid proteins from light-induced mature chloroplasts showed that the 58 kDa form was associated with the thylakoid membrane, behaving as a soluble or peripheral membrane protein. Two-dimensional gel electrophoresis discriminated, for the first time, the 58-kDa band in two different forms, probably corresponding to the two different TGase cDNAs previously cloned. Electrophoretic separation of thylakoid proteins in native gels, followed by LC-MS mass spectrometry identification of protein complexes indicated that maize chlTGase forms part of a specific PSII protein complex, which includes LHCII, ATPase and pSbS proteins. The results are discussed in relation to the interaction between these proteins and the suggested role of the enzyme in thylakoid membrane organisation and photoprotection. [source] | ||||||||||