Melatonin is a hormone synthetized from the amino acid tryptophan, whose central production is at pineal gland, which main function has been described as the synchronization of dark/light period in vertebrates. However, melatonin production in extra-pineal sites have been recently described in several tissues, such as: intestine, lungs and immune cells, by demonstrating several regulatory functions, including immune regulation. Once the pineal and extra-pineal melatonin production is modulated by molecular patterns associated to pathogens, its central production is diminished, while its local production, mainly in immune tissues, is increased in response to an immune challenge in mammals. Therefore, the investigation of extra-pineal melatonin production in different periods, as well as, its modulation by an immune stimulus in anuran amphibians, would represent an important contribution to the understanding of the process in this group, as well as, its degree of evolutionary conservation among tetrapods. The aim of the present project is to investigate if there is an independence in the melatonin production by pineal vs. extra-pineal sites in amphibians. Additionally, to investigate if the presence of an immune challenge induces decreased central melatonin production (detected in melatonin plasma levels), while increased extra-pineal melatonin (verified in immune tissues). For that, animals kept in a 12:12 dark/light cycle, will receive a lipopolysaccharide or saline injection at 10am and at 10pm and will be sampled 2 hours after the injection (12am and 12pm). Blood samples will be taken, for melatonin plasma levels quantification, and then the animals will be killed by decapitation, followed by tissue collection: bone marrow, lungs, liver and intestine to determine the melatonin present in the tissues.
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