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Berson, D. M., Dunn, F. A., & Takao, M. (2002). Phototransduction by retinal ganglion cells that set the circadian clock. Science, 295(5557), 1070–1073.
Abstract: Light synchronizes mammalian circadian rhythms with environmental time by modulating retinal input to the circadian pacemaker-the suprachiasmatic nucleus (SCN) of the hypothalamus. Such photic entrainment requires neither rods nor cones, the only known retinal photoreceptors. Here, we show that retinal ganglion cells innervating the SCN are intrinsically photosensitive. Unlike other ganglion cells, they depolarized in response to light even when all synaptic input from rods and cones was blocked. The sensitivity, spectral tuning, and slow kinetics of this light response matched those of the photic entrainment mechanism, suggesting that these ganglion cells may be the primary photoreceptors for this system.
Keywords: Human Health; Animals; Axons/ultrastructure; *Biological Clocks; *Circadian Rhythm; Dendrites/ultrastructure; Isoquinolines; Kinetics; Light; *Light Signal Transduction; Patch-Clamp Techniques; Rats; Rats, Sprague-Dawley; Retinal Ganglion Cells/chemistry/cytology/*physiology; Rod Opsins/analysis/physiology; Suprachiasmatic Nucleus/cytology/*physiology
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Bullough, J. D., Rea, M. S., & Figueiro, M. G. (2006). Of mice and women: light as a circadian stimulus in breast cancer research. Cancer Causes Control, 17(4), 375–383.
Abstract: OBJECTIVE: Nocturnal rodents are frequently used as models in human breast cancer research, but these species have very different visual and circadian systems and, therefore, very different responses to optical radiation or, informally, light. Because of the impact of light on the circadian system and because recent evidence suggests that cancer risk might be related to circadian disruption, it is becoming increasingly clear that optical radiation must be properly characterized for both nocturnal rodents and diurnal humans to make significant progress in unraveling links between circadian disruption and breast cancer. In this paper, we propose a quantitative framework for comparing radiometric and photometric quantities in human and rodent studies. METHODS: We reviewed published research on light as a circadian stimulus for humans and rodents. Both suppression of nocturnal melatonin and phase shifting were examined as outcome measures for the circadian system. RESULTS: The data were used to develop quantitative comparisons regarding the absolute and spectral sensitivity for the circadian systems of humans and nocturnal rodents. CONCLUSIONS: Two models of circadian phototransduction, for mouse and humans, have been published providing spectral sensitivities for these two species. Despite some methodological variations among the studies reviewed, the circadian systems of nocturnal rodents are approximately 10,000 times more sensitive to optical radiation than that of humans. Circadian effectiveness of different sources for both humans and nocturnal rodents are offered together with a scale relating their absolute sensitivities. Instruments calibrated in terms of conventional photometric units (e.g., lux) will not accurately characterize the circadian stimulus for either humans or rodents.
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Chaves, I., Pokorny, R., Byrdin, M., Hoang, N., Ritz, T., Brettel, K., et al. (2011). The cryptochromes: blue light photoreceptors in plants and animals. Annu Rev Plant Biol, 62, 335–364.
Abstract: Cryptochromes are flavoprotein photoreceptors first identified in Arabidopsis thaliana, where they play key roles in growth and development. Subsequently identified in prokaryotes, archaea, and many eukaryotes, cryptochromes function in the animal circadian clock and are proposed as magnetoreceptors in migratory birds. Cryptochromes are closely structurally related to photolyases, evolutionarily ancient flavoproteins that catalyze light-dependent DNA repair. Here, we review the structural, photochemical, and molecular properties of cry-DASH, plant, and animal cryptochromes in relation to biological signaling mechanisms and uncover common features that may contribute to better understanding the function of cryptochromes in diverse systems including in man.
Keywords: Adenosine Triphosphate/metabolism; Animals; Cryptochromes/chemistry/classification/*physiology; DNA Repair; Deoxyribodipyrimidine Photo-Lyase/chemistry/classification/physiology; Homing Behavior; Insects/physiology; *Light Signal Transduction; Magnetics; Mice; Oxidation-Reduction; Phosphorylation/physiology; Plants/*metabolism; blue light
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Foster, R. G. (2005). Neurobiology: bright blue times. Nature, 433(7027), 698–699.
Keywords: Human Health; Animals; Circadian Rhythm/physiology/radiation effects; Color Perception/physiology/*radiation effects; Humans; *Light; Light Signal Transduction/*radiation effects; Mice; Retinal Ganglion Cells/cytology/physiology/radiation effects; Retinaldehyde/chemistry/metabolism; Rod Opsins/*metabolism; NASA Discipline Space Human Factors; Non-NASA Center
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Jasser, S. A., Blask, D. E., & Brainard, G. C. (2006). Light during darkness and cancer: relationships in circadian photoreception and tumor biology. Cancer Causes Control, 17(4), 515–523.
Abstract: The relationship between circadian phototransduction and circadian-regulated processes is poorly understood. Melatonin, commonly a circadian phase marker, may play a direct role in a myriad of physiologic processes. The circadian rhythm for pineal melatonin secretion is regulated by the hypothalamic suprachiasmatic nucleus (SCN). Its neural source of light input is a unique subset of intrinsically photosensitive retinal ganglion cells expressing melanopsin, the primary circadian photopigment in rodents and primates. Action spectra of melatonin suppression by light have shown that light in the 446-477 nm range, distinct from the visual system's peak sensitivity, is optimal for stimulating the human circadian system. Breast cancer is the oncological disease entity whose relationship to circadian rhythm fluctuations has perhaps been most extensively studied. Empirical data has increasingly supported the hypothesis that higher risk of breast cancer in industrialized countries is partly due to increased exposure to light at night. Studies of tumor biology implicate melatonin as a potential mediator of this effect. Yet, causality between lifestyle factors and circadian tumor biology remains elusive and likely reflects significant variability with physiologic context. Continued rigorous empirical inquiry into the physiology and clinical implications of these habitual, integrated aspects of life is highly warranted at this time.
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