Thyroid Feedback to the Hypothalamic Neurosecretory System in Frog Larvae

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Abstract
In anurans the median eminence normally differentiates during early metamorphosis. It fails to differentiate in thyroidectomized tadpoles but appears when these animals are artificially metamorphosed by thyroxin. In the absence of the adenohypophysis no median eminence develops after thyroidization but in the hypophysectomized toads a pile-up of stainable material appears in the hypothalamus which is seen in the electron microscope to be composed of increased density of neurosecretory fibers. These results are interpreted as indicating thyroid feedback stimulating the hypothalamic neurosecretory system.