Light, Feeding and Melatonin: An Interplay in the Appetite Regulation in the Gut of Zebrafish (Danio rerio)

Every physiological function, including feeding and energy homeostasis is vital for animal sustainability. Melatonin is the neuroendocrine transducer of circadian photoperiod and is able to synchronize these physiological functions. The present study demonstrates the daily variation in gut melatonin and mRNA expression of appetite regulating hormone [leptin, nesfatin-1, orexin, ghrelin and ghrelin o-acetyltransferase (goat)] in relation to Gastrointestinal Somatic Index (Ga-SI) in the gut of zebrafish (Danio rerio), under various lighting schedule- LD (12L:12D), LL (continuous Light), and DD (continuous dark)- and scheduled feeding. The result exhibited a change in the peak level of the Ga-SI according to different photic conditions. But no change in Ga-SI was found after melatonin treatment under normal photoperiod (LD). Peak expression of anorexigenic peptide hormone genes (leptin and nesfatin1) were found with the highest level of Ga-SI but the highestlevel mRNA expression of orexigenic peptide gene hcrt was at the time of highest feeding and ghrelin with goat were after 6 hr of highest Ga-SI. These patterns changed in continuous photic conditions. This result indicates light as the critical dominant factor and, may be through melatonin, it can modulate the components of appetite regulation in this peripheral organ. This finding supports the hypothesis about the “light pollution” and its silent desynchronization of feeding behavior and related physiological functions, thereby the biodiversity and the sustainability of organisms.