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Batra, T., Malik, I., Prabhat, A., Bhardwaj, S. K., & Kumar, V. (2020). Sleep in unnatural times: illuminated night negatively affects sleep and associated hypothalamic gene expressions in diurnal zebra finches. Proc Biol Sci, 287(1928), 20192952.
Abstract: We investigated the effects of exposure at ecologically relevant levels of dim light at night (dLAN) on sleep and the 24 h hypothalamic expression pattern of genes involved in the circadian timing (per2, bmal1, reverb-beta, cry1, ror-alpha, clock) and sleep regulatory pathways (cytokines: tlr4, tnf-alpha, il-1beta, nos; Ca(2+)-dependent pathway: camk2, sik3, nr3a; cholinergic receptor, achm3) in diurnal female zebra finches. Birds were exposed to 12 h light (150 lux) coupled with 12 h of absolute darkness or of 5 lux dim light for three weeks. dLAN fragmented the nocturnal sleep in reduced bouts, and caused sleep loss as evidenced by reduced plasma oxalate levels. Under dLAN, the 24 h rhythm of per2, but not bmal1 or reverb-beta, showed a reduced amplitude and altered peak expression time; however, clock, ror-alpha and cry1 expressions showed an abolition of the 24 h rhythm. Decreased tlr4, il-1beta and nos, and the lack of diurnal difference in achm3 messenger RNA levels suggested an attenuated inhibition of the arousal system (hence, awake state promotion) under dLAN. Similarly, changes in camk2, sik3 and nr3a expressions suggested dLAN-effects on Ca(2+)-dependent sleep-inducing pathways. These results demonstrate dLAN-induced negative effects on sleep and associated hypothalamic molecular pathways, and provide insights into health risks of illuminated night exposures to diurnal animals.
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Zhang, X., Yang, W., Liang, W., Wang, Y., & Zhang, S. (2019). Intensity dependent disruptive effects of light at night on activation of the HPG axis of tree sparrows (Passer montanus). Environmental Pollution, 249, 904–909.
Abstract: Artificial light at night (ALAN) has become increasingly recognized as a disruptor of the reproductive endocrine process and behavior of wild birds. However, there is no evidence that ALAN directly disrupt the hypothalamus-pituitary-gonadal (HPG) axis, and no information on the effects of different ALAN intensities on birds. We experimentally tested whether ALAN affects reproductive endocrine activation in the HPG axis of birds, and whether this effect is related to the intensity of ALAN, in wild tree sparrows (Passer montanus). Forty-eight adult female birds were randomly assigned to four groups. They were first exposed to a short light photoperiod (8 h light and 16 h dark per day) for 20 days, then exposed to a long light photoperiod (16 h light and 8 h dark per day) to initiate the reproductive endocrine process. During these two kinds of photoperiod treatments, the four groups of birds were exposed to 0, 85, 150, and 300 lux light in the dark phase (night) respectively. The expression of the reproductive endocrine activation related TSH-β, Dio2 and GnRH-I gene was significantly higher in birds exposed to 85 lux light at night, and significantly lower in birds exposed to 150 and 300 lux, relative to the 0 lux control. The birds exposed to 85 lux had higher peak values of plasma LH and estradiol concentration and reached the peak earlier than birds exposed to 0, 150, or 300 lux did. The lower gene expression of birds exposed to 150 and 300 lux reduced their peak LH and estradiol values, but did not delay the timing of these peaks compared to the control group. These results reveal that low intensity ALAN accelerates the activation of the reproductive endocrine process in the HPG axis, whereas high intensity ALAN retards it.
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