Date of Award
Master of Science
Master of Biology
The metamorphic changes transforming the tissues of the tadpole into those of the mature frog are known to be under the control of thyroid hormone, that is, they fail to occur if the hormone is absent. However, it is becoming increasingly clear that control does not mean the determination of the specific character of the ensuing changes, but refers merely to the reactivated and further sustenance of different chains of morphogenetic events temporarily arrested in the larval stage, then continuing in each tissue reacting according to its own characteristics (Weiss and Rossetti, 1951). The importance of the thyroid gland as a controlling factor in metamorphosis is to be credited to Gudernatsch (1912) who fed horse thyroid gland to amphibian larvae and found that they showed an increase in metamorphosis. A great amount of work has been done along the line of experimental hyperthyroidism in the amphibian. The work of Allen (1916) and Hoskins (1917) on the removal of the thyroid gland in amphibian larvae clearly indicates that this gland is normally indispensable to metamorphosis in these forms.
In more recent years investigators have been concerned with direct action of thyroid hormone on various reacting systems (Kaltenbach, 1953a). Thyroid hormone has been shown to influence a variety of systems in the amphibian, including the nervous system. The nervous system responds to thyroid hormone by an increase in cell number (Kollros and Race, 1960; Race, 1961). Thyroxine also influences cell size (Weiss and Rossetti, 1951; Pesetsky and Kollros, 1956; Reynolds, 1963). Weiss and Rossetti (1951) reported a marked spurt in brain growth in Rana pipiens during metamorphosis, which is accompanied by intensified activity during normal metamorphic climax. A similar increase in mitotic activity has been reported by Martin (1962) in studies of normal development of the cerebellum in Rana pipiens, in young tadpoles immersed in high concentrations of thyroxine, and also by Reynolds (1966) in studies of the lumbo-sacral spinal cord of Rana pipiens larvae.
Various hormones, depending on their nature and degree of activity in the organism, exert a certain effect on the metabolism of nucleic acids. Mandel (1951) reported that after the injection of thyroxine (1 mg. per day) into rats, DMA content increased from 22 to 32% in the kidney. Similar increases in spleen ranged from 35 to 60% (Handel, 1952). A single injection of thyroxine into male mice has the effect of raising the proportion of DNA and proteins relative to MIA in the liver after 48 hours (Baxi, 1951).
E. W. Martin
C. E. Urdy
C. E. Urdy
J. E. Berry
C. L. Ward
Prairie View Agricultural and Mechanical College
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Date of Digitization
John B Coleman Library
City of Publication
Garner, L. A. (1967). The Effects Of Thyroxine On Deoxyribonucleic Acid Content In The Brain Of Rana Clamitans Tadpoles. Retrieved from https://digitalcommons.pvamu.edu/pvamu-theses/835