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Dauchy, R. T., Wren, M. A., Dauchy, E. M., Hoffman, A. E., Hanifin, J. P., Warfield, B., et al. (2015). The influence of red light exposure at night on circadian metabolism and physiology in Sprague-Dawley rats. JAALAS, 54(1), 40–50.
Abstract: Early studies on rodents showed that short-term exposure to high-intensity light (> 70 lx) above 600 nm (red-appearing) influences circadian neuroendocrine and metabolic physiology. Here we addressed the hypothesis that long-term, low-intensity red light exposure at night (rLEN) from a 'safelight' emitting no light below approximately 620 nm disrupts the nocturnal circadian melatonin signal as well as circadian rhythms in circulating metabolites, related regulatory hormones, and physi- ologic parameters. Male Sprague-Dawley rats (n = 12 per group) were maintained on control 12:12-h light:dark (300 lx; lights on, 0600) or experimental 12:12 rLEN (8.1 lx) lighting regimens. After 1 wk, rats underwent 6 low-volume blood draws via cardiocentesis (0400, 0800, 1200, 1600, 2000, and 2400) over a 4-wk period to assess arterial plasma melatonin, total fatty acid, glucose, lactic acid, pO2, pCO2, insulin, leptin and corticosterone concentrations. Results revealed plasma melatonin levels (mean +/- 1 SD) were high in the dark phase (197.5 +/- 4.6 pg/mL) and low in the light phase (2.6 +/- 1.2 pg/mL) of control condi- tions and significantly lower than controls under experimental conditions throughout the 24-h period (P < 0.001). Prominent circadian rhythms of plasma levels of total fatty acid, glucose, lactic acid, pO2, pCO2, insulin, leptin, and corticosterone were significantly (P < 0.05) disrupted under experimental conditions as compared with the corresponding entrained rhythms under control conditions. Therefore, chronic use of low-intensity rLEN from a common safelight disrupts the circadian organization of neuroendocrine, metabolic, and physiologic parameters indicative of animal health and wellbeing.
Keywords: animals; rodents; Circadian Rhythm; Light wavelength
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Dauchy, R. T., Xiang, S., Mao, L., Brimer, S., Wren, M. A., Yuan, L., et al. (2014). Circadian and melatonin disruption by exposure to light at night drives intrinsic resistance to tamoxifen therapy in breast cancer. Cancer Res, 74(15), 4099–4110.
Abstract: Resistance to endocrine therapy is a major impediment to successful treatment of breast cancer. Preclinical and clinical evidence links resistance to antiestrogen drugs in breast cancer cells with the overexpression and/or activation of various pro-oncogenic tyrosine kinases. Disruption of circadian rhythms by night shift work or disturbed sleep-wake cycles may lead to an increased risk of breast cancer and other diseases. Moreover, light exposure at night (LEN) suppresses the nocturnal production of melatonin that inhibits breast cancer growth. In this study, we used a rat model of estrogen receptor (ERalpha(+)) MCF-7 tumor xenografts to demonstrate how altering light/dark cycles with dim LEN (dLEN) speed the development of breast tumors, increasing their metabolism and growth and conferring an intrinsic resistance to tamoxifen therapy. These characteristics were not observed in animals in which the circadian melatonin rhythm was not disrupted, or in animals subjected to dLEN if they received nocturnal melatonin replacement. Strikingly, our results also showed that melatonin acted both as a tumor metabolic inhibitor and a circadian-regulated kinase inhibitor to reestablish the sensitivity of breast tumors to tamoxifen and tumor regression. Together, our findings show how dLEN-mediated disturbances in nocturnal melatonin production can render tumors insensitive to tamoxifen. Cancer Res; 74(15); 4099-110. (c)2014 AACR.
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de Jong, M., Jeninga, L., Ouyang, J. Q., van Oers, K., Spoelstra, K., & Visser, M. E. (2015). Dose-dependent responses of avian daily rhythms to artificial light at night. Physiol Behav, 155, 172–179.
Abstract: Recent studies have shown that animals are affected by night-time light exposure. Light is a continuous variable, but our knowledge on how individuals react to different light intensities during the night is limited. We therefore determined the relationship between night light intensity and the behaviour and physiology of great tits (Parus major). We measured daily activity patterns and melatonin levels in 35 males exposed to five different light intensities and found strong, dose-dependent effects. Activity onset was increasingly advanced, and activity offset delayed with higher light intensities. Furthermore, night-time activity increased and melatonin levels measured at midnight decreased with higher intensities. In this experimental study, we demonstrate for the first time dose-dependent effects of artificial light at night on birds' daily activity patterns and melatonin levels. Our results imply that these effects are not limited to a certain threshold, but emerge even when nocturnal light levels are slightly increased. However, in a natural area, these effects may be limited as artificial light levels are commonly low; light intensities drop rapidly with distance from a light source and birds can avoid exposure to light at night. Future studies should thus focus on examining the impact of different intensities of light at night in the wild.
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Deveson, S. L., Arendt, J., & Forsyth, I. A. (1990). Sensitivity of Goats to a Light Pulse During the Night as Assessed by Suppression of Melatonin Concentrations in the Plasma. Journal of Pineal Research, 8(2), 169–177.
Abstract: This study investigates the ability of a 1 h light pulse of different intensities at night to suppress plasma melatonin in goats. Six female Saanen dairy goats, about 2 yr old, were housed in a light-tight shed. The goats were habituated for 1 wk to an 8L: 16D photoperiod (40.70 ± 4.16 μW/cm2; 137 ± 14 lux), lights on 0800 h. A 1 h light pulse, of different intensity on each occasion, was given from 1900 to 2000 h. Light intensity was measured by using a lux meter (mean of 36 measurements at goat's eye level). Five different light intensities were given during December in the order 4.22 ± 0.62 μW/cm2 (14.2 ± 2.1 lux), 0.68 ± 0.09 μW/cm2 (2.3 ± 0.3 lux), 0.26 ± 0.004 μW/cm2 (O.87 ± 0.14 lux), darkness, 40.70 ± 4.16 μW/cm2 (137 ± 14 lux), with 1–3 d between treatments. The goats were bled hourly from 1500 to 1900 h and every 15 min from 1900 to 2100 h, and a last bleed occurred at 2200 h. Dark-phase samples were taken in dim red light (<0.03 μW/cm2; 0.1 lux). Plasma was assayed for melatonin by radioimmunoassay. Suppression of melatonin concentrations increased as light intensity increased as follows: Darkness, 0%; 0.26 ± 0.004 μW/cm2; 0%; 0.68 ± 0.09 μW/cm2; 43.1%; 4.22 ± 0.62 μW/cm2, 71.1%; 40.70 ± 4.16 μW/cm2, 81.2%. Suppression was significant (P<0.05) at light intensities >0.68 μW/cm2, 2.3 lux. A hyperbolic relationship existed between percent suppression and light intensities.
Keywords: animals; goat; Circadian Rhythm; Light intensity
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Dominoni, D. (2015). The effects of light pollution on biological rhythms of birds: an integrated, mechanistic perspective. J. of Ornith., 156(1), 409–418.
Abstract: Light pollution is considered a threat for biodiversity given the extent to which it can affect a vast number of behavioral and physiological processes in several species. This comes as no surprise as light is a fundamental, environmental cue through which organisms time their daily and seasonal activities, and alterations in the light environment have been found to affect profoundly the synchronization of the circadian clock, the endogenous mechanism that tracks and predicts variation in the external light/dark cycles. In this context, birds have been one of the most studied animal taxa, but our understanding of the effects of light pollution on the biological rhythms of avian species is mostly limited to behavioral responses. In order to understand which proximate mechanisms may be affected by artificial lights, we need an integrated perspective that focuses on light as a physiological signal, and especially on how photic information is perceived, decoded, and transmitted through the whole body. The aim of this review is to summarize the effects of light pollution on physiological and biochemical mechanisms that underlie changes in birds’ behavior, highlighting the current gaps in our knowledge and proposing future research avenues.
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