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Bedrosian, T. A. (Ed.). (2013). Circadian Disruption by Light at Night: Implications for Mood. Ph.D. thesis, , .
Abstract: Life on Earth has adapted to a consistent 24-h solar cycle. Circadian rhythms in physiology and behavior remain synchronized to the environment using light as the most potent entraining cue. During the past century, however, the widespread adoption of electric light has led to `round-the-clockâ societies. Instead of aligning with the environment, individuals follow artificial and often erratic light cycles created by social and work schedules. In particular, exposure to artificial light at night (LAN), termed âlight pollutionâ, has become pervasive over the past 100 years. Virtually every individual living in the U.S. and Europe experiences this aberrant light exposure, and moreover about 20% of the population performs shift work. LAN may disrupt physiological timekeeping, leading to dysregulation of internal processes and misalignment between behavior and the environment. Recent evidence suggests that individuals exposed to excessive LAN, such as night shift workers, have increased risk for depressive disorders, but the biological mechanism remains unspecified. In mammals, intrinsically photosensitive retinal ganglion cells (ipRGCs) project light information to (1) the suprachiasmatic nucleus (SCN) in the hypothalamus, regulating circadian rhythms, and (2) to limbic regions, putatively regulating mood. Thus, LAN has the potential to affect both circadian timekeeping and mood. In this dissertation, I present evidence from rodent studies supporting the novel hypothesis that night-time exposure to light disrupts circadian organization and contributes to depressed mood. First, I consider the physiological and behavioral consequences associated with unnatural exposure to LAN. The effects of LAN on circadian output are considered in terms of locomotor activity, the diurnal cortisol rhythm, and diurnal clock protein expression in the brain in Chapter 2. The influence of LAN on behavior and brain plasticity is discussed, with particular focus on depressive-like behavior (Chapter 3) and effects of SSRI treatment (Chapter 4). Effects of LAN on structural plasticity and gene expression in the brain are described, with emphasis on potential correlates of the depressive-like behavior observed under LAN in Chapter 5. Given the prevalence of LAN exposure and its importance, strategies for reversing the effects are offered. Specifically, eliminating LAN quickly reverses behavioral and physiological effects of exposure as described in Chapter 5. In Chapter 6 I report that administration of a pharmacological cytokine inhibitor prevents depressive-like behaviors in LAN, implicating brain inflammation in the behavioral effect. Finally, I demonstrate in Chapter 7 that exposure to red wavelength LAN reduces the effects on brain and behavior, suggesting that LAN acts through specific retinal pathways involving melanopsin. Taken together, these studies demonstrate the consequences of LAN, but also outline potential avenues for prevention or intervention.
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Bonmati-Carrion, M., Arguelles-Prieto, R., Martinez-Madrid, M., Reiter, R., Hardeland, R., Rol, M., et al. (2014). Protecting the Melatonin Rhythm through Circadian Healthy Light Exposure. IJMS, 15(12), 23448–23500.
Abstract: Currently, in developed countries, nights are excessively illuminated (light at night), whereas daytime is mainly spent indoors, and thus people are exposed to much lower light intensities than under natural conditions. In spite of the positive impact of artificial light, we pay a price for the easy access to light during the night: disorganization of our circadian system or chronodisruption (CD), including perturbations in melatonin rhythm. Epidemiological studies show that CD is associated with an increased incidence of diabetes, obesity, heart disease, cognitive and affective impairment, premature aging and some types of cancer. Knowledge of retinal photoreceptors and the discovery of melanopsin in some ganglion cells demonstrate that light intensity, timing and spectrum must be considered to keep the biological clock properly entrained. Importantly, not all wavelengths of light are equally chronodisrupting. Blue light, which is particularly beneficial during the daytime, seems to be more disruptive at night, and induces the strongest melatonin inhibition. Nocturnal blue light exposure is currently increasing, due to the proliferation of energy-efficient lighting (LEDs) and electronic devices. Thus, the development of lighting systems that preserve the melatonin rhythm could reduce the health risks induced by chronodisruption. This review addresses the state of the art regarding the crosstalk between light and the circadian system.
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Bullough, J. D. (2014). Spectral Sensitivity Modeling and Nighttime Scene Brightness Perception. Leukos, 11(1), 11–17.
Abstract: Brightness perception under different light sources is an important visual response, because it is related to perceptions of safety. A growing number of studies have been conducted to assess perceptions of scene brightness under light sources differing in spectral content, including results consistent with a role of melanopsin-containing, intrinsically photosensitive retinal ganglion cells in scene brightness. Data from recent studies of scene brightness perception at light levels experienced under nighttime driving conditions are used to compare different models of brightness perception. The data support a role of increased short-wavelength sensitivity for scene brightness perception and a provisional spectral sensitivity model that takes into account the possible influence of melanopsin-containing, intrinsically photoreceptive retinal ganglion cells is suggested as a basis for further investigation. The implications of such a model on brightness perception under several light sources used in transportation lighting are described.
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Cao, D., & Barrionuevo, P. A. (2015). The importance of intrinsically photosensitive retinal ganglion cells and implications for lighting design. J Sol State Light, 2(1), 10.
Abstract: We reviewed the role of melanopsin-containing intrinsically photosensitive retinal ganglion cells (ipRGCs) in light-dependent functions, including circadian rhythm that is important for health and visual perception. We then discussed the implications for lighting design.
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Foster, R. G., Hughes, S., & Peirson, S. N. (2020). Circadian Photoentrainment in Mice and Humans. Biology (Basel), 9(7).
Abstract: Light around twilight provides the primary entrainment signal for circadian rhythms. Here we review the mechanisms and responses of the mouse and human circadian systems to light. Both utilize a network of photosensitive retinal ganglion cells (pRGCs) expressing the photopigment melanopsin (OPN4). In both species action spectra and functional expression of OPN4 in vitro show that melanopsin has a lambdamax close to 480 nm. Anatomical findings demonstrate that there are multiple pRGC sub-types, with some evidence in mice, but little in humans, regarding their roles in regulating physiology and behavior. Studies in mice, non-human primates and humans, show that rods and cones project to and can modulate the light responses of pRGCs. Such an integration of signals enables the rods to detect dim light, the cones to detect higher light intensities and the integration of intermittent light exposure, whilst melanopsin measures bright light over extended periods of time. Although photoreceptor mechanisms are similar, sensitivity thresholds differ markedly between mice and humans. Mice can entrain to light at approximately 1 lux for a few minutes, whilst humans require light at high irradiance (>100's lux) and of a long duration (>30 min). The basis for this difference remains unclear. As our retinal light exposure is highly dynamic, and because photoreceptor interactions are complex and difficult to model, attempts to develop evidence-based lighting to enhance human circadian entrainment are very challenging. A way forward will be to define human circadian responses to artificial and natural light in the “real world” where light intensity, duration, spectral quality, time of day, light history and age can each be assessed.
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