A recurrent theme in the field of neuroendocrinology is that coordination of physiological processes is involved in regulatory responses. It is well known that specific hormones may control physiological events and be responsible for the control of appropriate behavioral actions. In mammals for example, angiotensin II (A-II) acts peripherally to influence water balance and centrally to regulate drinking behavior. However, the exact central mechanism of action of A-II on drinking behavior is still not well understood. In general, amphibians are highly dependent upon regular and predictable sources of water. Peptide hormones such as arginine vasotocin (AVT) and angiotensin (A-II) can influence water balance by acting on skin, internal organs, and by influencing behavior. Amphibians obtain water through cutaneous absorption from a pelvic patch of skin. Frogs display water-absorption behavior by moving to and placing their ventral skin against a moist substrate. The strong and predictable display of this behavior makes frogs an excellent model to study the influence of peptides on water absorption behavior. Furthermore, because these hormones have other peripheral actions on water-balance, these model systems may help elucidate the coordinated action of hormones on peripheral organs and central nervous system targets. The purpose of this study is to elucidate the role of A-II and AVT in the water-balance. The specific goals of this project include determining 1) whether dehydration induces water absorption behavior in a mesic-dwelling frog species (R. pipiens), 2) whether AVT and/or A-II and their antagonists influence water absorption behavior, 3) where in the central nervous system and in peripheral tissues the hormones are located, 4) whether dehydration causes the release of the hormones into the general circulation, and 5) whether there is an interaction between the two hormones.
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