Abstract
Circadian rhythm in all living organisms is disturbed continuously by artificial light sources and artificial lighting has become a hazard for public health. Circadian rhythm of melatonin maintains high levels of melatonin during the night and low levels during the day. N-acetyltransferase (arylalkylamine N-acetyltransferase, AANAT) is one of the four enzymes required for melatonin synthesis and mtnr1ba is a melatonin receptor-encoding mRNA that is expressed widely in the embryonic brain. Pax7 has important roles during neural crest development and especially xanthophore pigmentation. Due to its diurnal nature, zebrafish provide a special opportunity for research on circadian rhythms that are regulated by melatonin. Here in this study, we showed that when compared with the white light control group, white LED light exposure resulted in loss of yellow pigmentation, decreased body length and locomotor activity, oxidant-antioxidant imbalance and decreased expressions of aanat2, mtnr1ba, and pax7 in zebrafish embryos. Histological analysis of this group revealed disorganization of the spaces among photoreceptor cells, decreased total retinal thickness and photoreceptor cell layer thickness compared with the control group. Artificial lighting pollution has the potential to become an important risk factor for different diseases including cancer especially for industrialized countries, therefore, more studies should be performed and necessary regulations should be made regarding this risk factor.
Highlights
Sunlight is a major factor in the maintenance of the biological clock and the regulation of the circadian rhythm in all living organisms
The results of our study show that artificial lighting using Light emitting diodes (LED) affected the morphology, mortality and hatching rates, locomotor activity, oxidant and antioxidant parameters and gene expressions related with melatonin circulation, mtnr1ba, and aanat[2], as well as pax[7] which is an important regulator of xanthophore production in zebrafish embryos
Nocturnal pineal melatonin generation is very photosensitive to the light with short wavelength such as blue light[25,26]
Summary
Sunlight is a major factor in the maintenance of the biological clock and the regulation of the circadian rhythm in all living organisms. In the pineal gland circulating melatonin is produced which acts as a hormone in seasonal and circadian physiology and the melatonin produced in retinal photoreceptor cells is suggested to regulate light and darkness adaptation. Melatonin is produced in the adult pineal gland of zebrafish regulated by a pineal circadian clock upon the action of light on pineal photoreceptors[8,9,10]. Recent studies have shown that artificial light exposure affects cell differentiation, growth, and development and cause cardiovascular diseases, diabetes, obesity, neurological diseases due to changes in the endocrine system as well as different types of cancer[4,13,14,15,16,17,18,19,20]. The role of the light spectrum has not been extensively investigated in zebrafish
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