The cardiovascular control is related to the appropriate oxygen delivery to tissues, according to the metabolic demand of the organism. To ensure the correct supply of oxygen carried by the blood there is a control executed by the autonomic nervous system with its sympathetic and parasympathetic branches. At the embryo phase, the nervous system is in continuous maturation and the mechanisms used for cardiovascular control are not well understood in the group. In reptiles, the oxygen demand changes during embryonic development due to tissue formation and embryo growth. Previous studies show that the oxygen consumption in embryonic reptiles rise along the development in three possible patterns: exponential, sigmoidal and in peak. Thus, cardiovascular adjustments occur throughout the embryonic life, in order to match the oxygen demand of each stage. In this study, the metabolism (VO2), the mechanisms of control of the heart rate by the autonomic nervous system and the localization of the vagal nerve projections in the brainstem will be determined in different embryonic stages and in juveniles or adults of two lizard species, Iguana iguana and Tupinambis merianae. These species are from distinct clades of the Squamata phylogenetic tree. As reptile eggs are susceptible to environmental variations, it will be also determined temperature and gas composition effects in heart rate at the last stages of development.
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