Hypothalamic Sensitivity to Thyroid Feedback in the Tadpole

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Abstract
The differentiation of the median eminence in the thin floor of the hypothalamus had been shown to depend on thyroid hormone feedback in the frog larva. Itis demonstrated here that the median eminence region is not sensitive to thyraxine until the animal reaches a late tadpole stage. From this fact it is inferred that the time of metamorphosis depends on genetic factors that regulate the acquisition of sensitivity to thyroxine by the hypothalamus. The pattern of subsequent metamorphic changes however is regulated by a spiraling feedback system. The hypothalamus stimulated the pituitary which stimulates the thyroid which then feeds back again to the hypothalamus.