Title: The effects of posterior hypothalectomy upon the growth and metamorphosis of the tadpole of Rana pipiens
Abstract: In Rana pipiens the removal of the posterior hypothalamic preprimordium at the open neurula stage resulted in the development of light-colored tadpoles. The hypophysis of the hypothalectomized tadpole lacked a pars intermedia but it had a pars distalis of varying size. The growth of hypothalectomized tadpoles proceeded as in intact tadpoles, whereas hypophysectomy resulted in marked delay in growth. The hypothalectomized tadpoles were characterized also by a marked delay in metamorphosis from the premetamorphic stage. Their thyroid glands were noticably smaller and the mean height of the follicle epithelium of the thyroid gland was much lower than in normal tadpoles. Most of the hypothalectomized tadpoles never exhibited the protrusion of forelimbs, the absorption of the tail and the other phenomena seen in the metamorphic climax. The incompletely metamorphosed tadpoles continued to grow and became approximately twice as large as the normal ones. On the basis of these experimental results, discussions were carried out on the mechanism of morphological differentiation of hypophyseal components, as well as the secretion of hypophyseal hormones under the control of the hypothalamus during metamorphosis. It was concluded that, while the pars distalis is self-differentiating, the embryonal differentiation of the pars intermedia is under the inductive influence of the infundibulum of the brain. Posterior hypothalectomy, involving removal of the median eminence, interrupted the transmission of stimulatory influences from the brain, and prevented elevated TSH secretion in the hypophysis. This, in turn, suppressed the release of an increased amount of thyroid hormone during the metamorphic climax. The secretion of growth factors from the hypophysis, on the other hand, seemed to be unaffected by the posterior hypothalectomy.
Publication Year: 1967
Publication Date: 1967-06-01
Language: en
Type: article
Indexed In: ['crossref', 'pubmed']
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Cited By Count: 42
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