Interaction of the Plasma Melatonin Rhythm with other Hormone Rhythms During Development and on Various Light/Dark Cycles

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Metamorphosis of the amphibian tadpole is a developmental program driven mainly by an increased secretion of thyroid hormones, although other hormones, such as adrenal corticoids, prolactin, and melatonin may accelerate or inhibit its progress. Many hormones exhibit rhythmicity, and peak in the blood at specific times of the day. Differences in the timing of the peak level of various hormones could be critical to the regulation of metamorphosis. However, the rhythm of hormones in the plasma of tadpoles is not known. Using radioimmunoassay, this project will study the circadian rhythmicity of the metamorphic hormones mentioned above in the plasma of tadpoles from early to late stages of development. Tadpole development rate is also dependent on the light/dark cycle, as are plasma melatonin levels, which are higher in the dark. Melatonin inhibits the thyroid gland of tadpoles, as well as the tissue response to thyroxine. This research will also focus on the relationship between the light/dark cycle and thyroxine and melatonin levels and rhythms. This work will further understanding of the role of hormones in development, especially the influence of melatonin. Since the secretion of melatonin is related to light and darkness, the research will also help us to understand the influence of the environment on amphibians. This is a problem of much concern in view of the recent appearance of frog abnormalities, some of which appear to be developmental in origin. The work will be done at an undergraduate institution with the collaboration of undergraduate researchers, who will be introduced to the scientific process in preparation for professional and scientific careers.